I am currently building a 30 x 48 with 12 foot tall walls metal sheeted building. There is also a wrap around small porch on the front, two 30 50 windows, and two 30 00 doors and two 9x9 foot garage doors. There is a 30 x12 foot gravel lean too on the back.

The footers for the concrete pad and stem wall are curing now. They were poured on Friday. I plan on the exterior walls being 2x6 framed on 24 inch centers. I am using trusses for the roof. I have an Amish crew that is going to do the framing and metal sheeting. I planned on the trusses being on 2 foot centers. They said that for my area, I could save a bunch on money by doing 4 foot centers on my trusses since they are engineered trusses.

We dont get alot of snow here in Lebanon, MO (SW Missouri) but, I dont want the roof caving in either. What will I loose by going to 4 foot centered trusses? Will I be less resistant to high winds or snow load? Or is 4 foot common now and I am over building???

Your local building code should specify a snow load in pounds per square foot and the trusses spec will determine truss spacing.

This. And piece of mind is very underrated.

You mean to check the local city build code? There is no code, permits or inspections in the county here.

Your trusses will be designed to some parameter, probably somewhere around 30LL-10DL-10DL @ 2’-0” OC. If you space them at 4’-0” on center, you’re cutting your loading in half or 15LL-5DL-5DL.

Based on your situation, put them 2’ o.c.

This, peace of mind is worth a lot

Back in the day, there were no permits or codes for the rural areas outside of city limits here in the central and eastern UP. During the extremely heavy snowfall during the winter of 2018-2019, over 250 shed and garage buildings collapsed. Some had survived 30 to 40 winters before the big one. Our Cleary engineered and built 36 x 48 x 14 wall pole building didn’t even creak or groan with the snow load. Peace of mind is priceless.

Yep the extra cost of a few trusses is nothing in the long run
Another good idea is to upsize all lintels, small cost but less deflection makes a building look much better in the future

Insulate it if you can, it will be amazingly cooler in the summer.

No offense, but that is not a metal building.

most pole barns in this area the trusses are on 5/6 foot centers. I am about 100 miles north of you.I built a pole barn home in 2004 and my trusses are on 5ft centers

Talked to a buddy who used to build them, don't have to worry about snow, but I'm planning on a car lift, and maybe a mill. he told at least a 6-inch fiber reinforced slab. Might go big enough to build a decent side home inside of it, a barndominium. and try to keep it ag so I'm not paying a lot of property tax. get a few goats, the old lady has always wanted a couple of goats.

Make it big----er!

My son has a 40x50' garage/shop on his property. His wife rented a building in Slater Iowa where she cut hair. The derechio in August damaged the building so he had to build her a hair salon inside of his garage. It takes up about 20% of the floor space and blocks one of his over head doors. I'm sure he wishes he could do that garage 50x50 right now.
kwg

Insulate it for sure if you are thinking of building living quarters in it.

And don't cheap out on the wall framing, either. Go 16" centers and forget the 24" BS....

Every pole barn I've ever built or seen had 8' spacing on the rafters with 2x4 purlins between them. Seen every pole barn/shop but that way from Minnesota to new Mexico. How much snow do you get in Missouri?!?!

I'm guessing you are building it similar to a house and sheeting it with OSB on the roof? In that case I have no idea. Given the cost of building materials though I'd be looking to save wherever I could and pencil it out. Maybe check with a local building engineer?

Most pole barn and metal building roofs are on a low pitch- go to a 6/12 pitch with metal roofing and leaves/snow will slide right off- mine is on 4' centers. 42x42 stick built with no trusses.

I think you would be amiss to not go with 10' garage doors if you can fit em in... As far as the framing, I like the pole barn layout , but your plans are totally fine. 2' OC on the walls is plenty and I would run a double top plate, but beauty is in the eye of the beerholder! Make sure you hurricane clip all the trusses to the top plate, as some areas do not. One cannot over sway brace the inside of the trusses either, just sayin!

+1 on the garage door size. Full size pickups are about 8' wide with towing mirrors and some trailers are 8' 6" wide. 10' x 10' or 10' high x 12' wide doors would make for easy access.

Consider putting a garage door on the back side. Sure is nice to take lawn tractors, ATVs, etc. in and out of the shop without moving the vehicles parked inside the main garage doors.

I would at least put in the tallest doors you can. 14' sidewalls will allow 12' doors and be a lot more user friendly. Insulation is a must. Whatever space you think you need you can multiply by two and still be too small.

Sounds like you are going to put up a wood framed building with steel siding. There is nothing wrong with that except it is not really a metal building. I have built several steel framed, steel sided buildings and there are a few suggestions I would make. Have the trusses designed for whatever spacing you choose. Trusses designed to be placed on four foot centers will probably be a little more expensive than those designed to be placed on two foot centers. Then decide.
The size of the windows doesn't make much difference. The placement will be more of an issue because it will affect the use of wall space and air flow inside the building. The twelve foot wall height is adequate for most uses but it might not be high enough for a lift. If you have plans to work on any kind of heavy equipment you might consider going 16' high at least. In my opinion, the doors you have planned are too small. I would go at least 36" wide on the walk through doors and 12' wide on the garage doors. Roll up doors would work very well, but if you go wider than 12 feet they have to be built to withstand windload and start getting very expensive. Roll up metal doors 12' by 12' would be just right unless you plan to work on combines or swathers.
Rainshot gave you good advice. I am just expanding on what he said.,

Insulate the entire building and insulated OH doors. When they pour the slab have them lay a 2x10 down flat for a pocket for the OH door to sit in so water doesn't blow under the door.

Now we are getting someplace. Some random thoughts that are worth what you paid.
Truss spacing has nothing to do with roof load if you are using an engineered package. Wider spacing equals heavier trusses. Price both and compare. The ceiling you install will dictate the nailer spacing. Sometimes closer is cheaper. You cannot take the same truss and widen the layout without compromising the values.
I have not put in a 9' wide overhead door for 20 years. The difference in cost for at least a 10' is far cheaper that replacing an electric/heated mirror once. With kids driving also I think you understand.
Consider house wrap under the steel panels. Steel will leak a lot of air when its breezy.
A 48" wide walk door is 100 bucks more that a 36". If that will let your mower etc. pass without opening a larger door its probably worth it. If you want a little more room a 6' x 7' overhead is much cheaper than a double walk door.
Length is cheaper than width as you have already bought both ends.
In my shop the car lift works just fine with a 12' ceiling unless you opt for the heavier bus rated ones. Possible a raised lower chord truss is an option.
If you go with the shorter doors consider a vertical lift track so the horizontals are not hanging down below the ceiling. Jackshaft operators work well with this system.
Insurance is considerably less with UL listed steel. (30% or more)
When I install radiant heaters I will try to utilize a raised lower chord truss mentioned above to allow more room for the unit to be installed. No fun to melt stuff parked underneath of it.
Prep for gutter even if you never install it,
For the most efficient building we use SIP panels. If you are going to climate control the interior its the best route.
Be sure to taper the concrete under the overheads or water will run in vs out.
Good luck

Codes may not apply being outside city limits, but are often a good guideline.
Man doors should be 36”, not 30”.

Ha ha lot's of people "want" goats until they don't. Heck I want fainting goats because I think a cooler of beer and a gross of bottle rockets would be an excellent way to pass the time. lol

But goats are destructive critters.

I have friends that got a couple. They had them less than a week and got rid of them after they walked all over the vehicles, chewed the new siding off the house, the tin off the shop and started at one corner of their new sidewalk and chewed a big chuck out of the concrete.

They were PISSED!

I LMAO.

I've dealt with before.

Maybe I missed something.
Is the a pole barn or stick frame?
My pole barn in Northern Idaho has the pole 10' on centers 6X8 treated corners 8x8 same for trusses 2X6s 2' on centers between truss. Snow load at 60 pounds per sq ft.
Side wall are 2X6s horizontal every 2'
It's 50 x 36 with two 12 X 14 doors, I can get anything I want inside.
Sorry but 9x9 doors is stupid. Never get much inside except a pickup. or small boat.
Bigger is better.
/We looked at a lot of places before we bought this place with shops with small door low ceiling can't get much inside.

Concur on the bigger doors, my 30x50 shop has 36" entry doors and the rollup door is 12', I wouldn't want them any smaller. 9' wide is definitely too small.

I'm not in a heavy snow part of this state, but all the metal barns here have trusses every 8-9' with purlins including mine that we built. We do get some extremely high wind events and it remains unphased. When we were putting the roof tin on my friend and I were both standing on the same piece of tin so well over 400lbs total. Wasn't and isn't an issue.

If you have flat trusses and are going to put a ceiling up go on 2ft centers. Makes it a lot easier for rock or plywood. Just double check the rat runs and make sure they are on two foot centers. It sucks to add blocking afterwards if they don’t know how to pull layout. I have a 4/12 pitch on my 30x52 shop and a 4/12 on my 36/60 shop. Both are rated at 140 pounds a square foot. One of the shops is two foot on center. The other is larger trusses and purlins. Will they run sheeting or skip sheeting?

Why ya gotta go and bring up engineering?

These Campfire guys know everything.
Their so busy telling him how big of doors he needs that they haven't even got to the part about how all metal buildings sweat inside yet.

They don't need no stinkin' Engineer telling them what to do.

You f u c k s kill me .

Not a single one of you (save one) knows what a metal building is.

What you describe to to op is a flattened structure when I look at regional wind loads for him. I hope his wife and kids get away.

My building is steel. Designed for 175 winds. L/400. 30 psf live load no reduction. 10 collateral.

C [bleep] bang bang for your buildings

I have a 65x32 shop with 16’ walls. I didn’t “need” 16’ or the 14x14 roll up doors but I figured if I ever change my mind or decide to sell you can get a full size RV or semi truck inside if you wanted to. Also the extra height allows me to add some upstairs storage if I ever decide to.

Thank the lawd you chimed in and saved the OP’s family !!