Question [Q] I want to build a rom... well kinda

I want to take a pre-existing rom apart, mod it to what I want and rebuild it. Where do I begin? I have got a Linux Mint computer that will be dedicated to this. I have looked at Android Kitchen, but see no support for it anymore. I want to learn how to build roms for our Notes, just need fingers showing me how. OH and before I get flamed I have done alot of googling on the subject and don't know what to do specifically for our phones. I am asking for help.