As far as chewing on plastic, I used holes that were small enough that I didn't think she'd be able to get her teeth at the edges to gnaw easily but I do intend to keep an eye and will upgrade her as necssary.
i should have been more specific i guess. rats can eat through plastic,wood,cement and certain metals. it does not matter if there are holes in the plastic or not. i am more concerned about air circulation though. rats can get really gnarly skin and respiratory problems from not getting enough circulation. aquariums have the same problem. i have a really good rat food recipe, if you want it pm me.