you can make firearms, that is legal. making them to sell without the manufacturing license is a big no-no. IMO, i say build it. let us know how it turns out and what you learned. a separate thread about your experience would be cool. i've thought about doing a pistol 80% or 10/22 80%, but haven't done it. i've done a couple of 80% AR lowers and they were pretty easy with my jig. homemade guns do not require serial #'s, but are a good idea.
i wouldn't carry it though. i don't trust my handiwork to save my life. i'll put my life on the line with proven firearms and proven self defense ammunition. YMMV.