I'm a newb, searched the site, didn't come up with anything.
Thinking of building one, might would be better off buying built. Love to tinker though.
built as in?
wanna build from scratch?
build a lower and slap an upper on it?
slap upper and lower together?
the hometown forum would be a better place for this imo.
but heres what i have seen.
topgun has rockriver arms matched upper and lowers along with "bushmaster" bolt groups and little things here and there
coz_45 is a dealer and has lowers and lower parts kits for great prices and also does ffl transfers for the houston crew. i imagine he could also source whatever else you might need.
you can find coz in the industry forum under northwest houston tactical.
other than that i usually just order from one of the site supporting dealers here.