There are a couple of from scratch project threads here on the forum. I'm not exactly sure where they are. One was an AR build and one was a 1911 build. If you can find them, I'm sure they'll be very informative.
Do you have precision machining experience and equipment?
“If ye love wealth better than liberty, the tranquility of servitude better than the animating contest of freedom, go home from us in peace. We ask not your counsels or arms. Crouch down and lick the hands which feed you. May your chains set lightly upon you, and may posterity forget that ye were our countrymen.” ― Samuel Adams