I remember one of my mother's uncles, at a picnic, responding to a comment about a proposed gun ban with a laconic "Doesn't matter. We'll build our own." Building rifles was his hobby, I learned during that day of grilling and shooting on his land in long-ago rural New Jersey. His comment has come back to me over the years, especially after, for Christmas, my wife gifted my son and I a jig for completing an unfinished AR-15 lower receiver. Like my great uncle, we built our own. We recommend the experience.
Making personal firearms is perfectly legal under federal law, if that matters to you, though states and localities may have their own rules. To that end, finishing "80 percent" receivers has become a popular pastime since the roughed-out blocks, shaped like the part of the AR-15 rifle that contains the hammer, safety, and trigger, but with solid material where those parts should fit, can be purchased without the legal rigmarole required for buying a firearm (the privacy offered by a DIY gun is somewhat compromised if you then write an article about your activities). It's a modern version of my uncle's hobby, simplified by the use of jigs that guide drill bits and end mills for finishing the project.
My wife gave us the Easy Jig sold by 80% Arms, which is one of a number of competing products in that category. I've only ever done this once, so I can't tell you which jig is best, but the Easy Jig got the job done, and came with clear and concise instructions that made our obsessive viewing of the online instructional video probably a bit superfluous.