Lib Logic 101

It is not illegal to make your own gun. It is illegal to transfer it in any manner - even if given as a gift - let alone to kill someone with it. Look up "80% lowers" or "stripped lowers" for AR-style rifles, for example.

not exactly true, either

you can't make a gun with the intent to sell it, but so long as it meets legal configuration requirements as a firearm and is properly marked with maker information and a serial number a homemade gun can be transfered

the devil is in how long you have to own it as a "completed" firearm to prove you weren't making it with intent to sell before you transfer it

this is not legal advice, your mileage may vary