It's going to cost more than you have budgeted, take more time, and it won't be big enough... I can see I already need more space... noticed that before the slab was cured....
I'm working on a 32X40 with 16 foot walls, heated slab, 2 garage doors (one 12X12), bathroom - sans bath. Had contractors do the slab, framing, siding, roof installation, ceiling drywall, and garage door insulation. Still need contractors to do the boiler (on hand) hook up - including gas line from the house hook-up. I'll probably have him do the basic PEX bathroom plumbing at the same time. Also need a contractor to blow in ceiling insulation. Those two jobs are gonna cost upwards of $7K, I think. Then I can finish the beast off myself, given time and money.
I still need to finish some of the outside trim and inside wiring, wall insulation, inside wall sheeting and finish, install ceiling lights (on hand), and Epoxy (on hand)seal the bathroom floor. I probably have nearly all the remaining wiring stuff I need. Do not have the rest of the insulation, nor interior wall coverings (I want to back the sheetrock with 1/2 inch plywood - but may forgo that...). Also there will be a partial loft over the bathroom and part of the garage space, with outside entry from the future greenhouse on the hill side, at the 8 foot wall level. I originally designed it with 14 foot walls, but had to go with 16 to get the greenhouse door to fit - cost me another $200 in materials, but probably saved more than that in labor just not having to cut the T-111.
I designed this to be fairly readily convertable to a complete house, or a couple rental apartments in the future if wished or necessary.
I've burned thru the original $75 K budget already, plus a few K out of pocket, doing as much of the work myself as I felt competent to do and had the time for. (Kinda hard when one is living 500 miles away at the time.... :)).
Outside, I still have a bit of retaining wall, backfill, a partial loft, and then a heated-slab attached greenhouse in the future. Also a couple of the house windows to install, as we need to replace those- they are 5X8's so aren't going to be cheap, either. But the garage is enclosed and usable right now, even if unheated.
If I don't die first, and if I can keep the wife employed, I'll get this thing done yet... It's been a decade in the planning and implementation so far, probably take another one to finish, financially.
That should give you an idea of what you are getting into, here, Joel...