Custom game idea

Hi i was wondering why aren't we able to play all the champions for free in custom games? I, like many other people don't have all the champions in the game nor enough IP/RP to get them all. I would like to play a bunch of champions to test them out but they aren't always in free champ rotation and i don't want to wait for what could be a month or two for it to be in there. I hope that if a dev see's this they at least consider it. thanks for taking the time to read this and have a good day. :D