Where can I get the go/no go gas checks?
Are you looking for head space gauges? First thing I would do is some research. Find out what the factory spec is supposed to be on the gun, as the SAAMI specs may be tighter. I'll leave it at that. Anyway, if your gun is 7.62x39, Midway USA has them. I've yet to run across one for the 5.45 caliber.
Anybody do a lot of building? Any websites that are helpful?
Wish I kept a lot of the information I had. I did dig up a video on YouTube that shows how to bend your own receiver. You'll need the right jigs and a press, but I suppose it would be worth it if you were planning on building a lot of them. The video isn't a complete reference on its own, but it is nice to have to illustrate what is being described in written instructions.
EDIT: The AR15.com DIY forums are a good place to start:
http://www.ar15.com/forums/forum.html?b=4&f=51