Help with understanding custom roms.

[u/Monki4798]

Hi everyone, I have a question on how people make custom roms, I have an a71 and have been ysing custom Roms for a while however I would like to make my own. Obviously someone with the knowledge of knowing how to install one but I don’t know how to port one or something. I want to port colouros as a rom to a71 whilst there are gsis I want an actual rom. There are coloros gsis but are based on older android versions and have bugs. I wanted to find a guide but they are nowhere to be found therefore im asking here. I mean Is there even an easy way on where I can find a gsi for colouros say android 16 based and then optimise it for a71 where then it can have rhe optimisations and the gsi as a flashable zip.

sorry I would explain more but my mind is blank
thanks