It is perfectly legal to make your own guns, as long as you DO NOT INTEND TO SELL THEM. If you intend to sell them, you need a manufacturer's license. You can legally make guns for your own use as long as they don't break any already existing legislation such as barrel length, whether they are semi-auto or full auto, etc.
Here is the site you need to read:
Home Gunsmith Forums
And, a slight correction. You CAN build your own suppressors, AOWs, SBSs and SBRs IF you can legally own one AND you file a form 1 and pay your tax first.