no no no no it's the roms that are illegal to use if you don't have the game... but this emulator will be a custom system made by me. and the roms will be custom made as well.
also if someone(yes my emulator is made to read custom roms from other ppl...) makes a copyrighted rom(like from nintendo, atari, CD64, or zega games) for my emulator i'm not the one to blame. the rom maker is to blame if the rom they make is copyrighted.