I have a Big Agnes Copper Spur tent and would like to make my own footprint that includes the vestibule area as well, as well as make a summer rainfly that allows more air to pass through.

Where is a good place to find quality lightweight materials for this?

Will a standard cheapy sewing machine be able to handle the sewing? SWMBO thinks not.

Tyvek makes a great footprint - and you can get it in smaller quantities on ebay. As for the fly, you might look into silnylon or cuben, but I don't have experience with sewing those materials. Good luck!

+1 on the Tyvek foot print.
Try Rockywoods for the fabric.

http://www.rockywoods.com/

Here is another source with good prices.
backwoodsdaydreamer.com

rodwha, a standard sewing machine should handle it no problem. try to run a heavier thread like the 69 pound "upholstery thread" sold in every fabric store.

Use tape for tyvek though. Sewing tends to make perforated tear lines...

I use tyvek cut a bit small and make the tabs for the poles out of duct tape. I add grommets for the poles.

Here are a couple more sources for fabric plus all the hardware & accessories you might need.
SEATTLE FABRIC
QUEST OUTFITTERS

Thanks fellas!
I've e-mailed Big Agnes to see if I can purchase the attachments for the footprint that you would set the tent poles in and hook the fly to. Not a big deal, but I'd like to be able to set it up without the actual tent as you can with the footprint & fly.

I've been told by others to just use a painter's drop cloth, but I wonder about it's durability. I enjoy figuring this kind of stuff out, but I don't care to do it over and over and over again.

I don't think the drop cloth would last at all. They're only about 4 mil at the heaviest. The Tyvec is much stronger for it's thickness. Go to ebay and search 'tyvec sheet'. You'll get a bunch of hits for both large sheets and also precut sheets just for tents. Those will often come with grommets or loops you can install as needed. I looked at a 9x10 that will fit our car camping tent. I can get one for about $15.

With my tyvek, gorilla tape/grommet setup......you can pitch just the fly.....unless it was Texas hot out.

I contacted Big Agnes and was surprised that they would sell me the attachments for the tent poles/rainfly clips.

Out of curiosity what is Tyvek precisely? I've looked at the links I've been given here and don't see it listed as Tyvek. I did ask what they thought would suffice for my intended purpose and got a few answers.

Guess it's time... $70 for a small piece of tarp just seems ridiculous.

Tyvek is a waterproof membrane that's used for lots of stuff. You'll see it as house wrap on new buildings to stop moisture from getting through the walls. It's used for coveralls for handling chemicals and asbestos because it prevents contamination. It's even used for mailing envelopes. Have you ever ordered an item of clothing that came in a plastic mailing bag that needed scissors to open because it's too tough for your teeth? That's Tyvek.
While it's very thin and light, it's also very tough.