Building your own from the 80% lower is still even allowed in California if you can believe that.
The laws did change last year, and I don’t recall the changes but I believe there was a cutoff date to get you home made guns serialized without having to register them. After that date I believe you had to register the lower on an AR-15 and other builds. Also a mag lock is required but entrepreneurs have mitigated that with slick quick releases which videos of can be found on YouTube.
I don't think that is right. I believe that if you owned a homemade gun just prior to the effective date of the law that you had a choice. You could put your own markings on it but were then required to register it. Alternatively, you could apply to the state for a serial number and apply that number to the firearm, thus registering it.
For firearms made after the effective date of the new law, the only option is to request and receive a serial number prior to beginning the build.
If I'm wrong about this I welcome any corrections.
If you wish to have the "evil features" of an AR15, then you have to have a fixed magazine. There are, I think, several ways to accomplish this.
If you are willing to give up the pistol grip, the adjustable stock, the flash suppressor, and any forward grip, then you can continue to operate the rifle using detachable magazines. (There may be some "evil features" that I missed, like a barrel shroud, etc. Best to check this carefully.)