As some of you may or may have not read, I am going to be two rats within the next few months. (Well, as soon as I get a job.) And since i'm mostlikely going to be making minimum wage ($7.50 where I live, and i'm sixteen.) i'll need to be as cheap as possible, but still make sure everything is rat friendly. But I got to thinking, and I figured that I could turn my bookshelf into a rat cage. I've seen it done before, and i'm sure that it would be fairly simple. So, can anyone explain to me what i'd exactly need to do to make everything a great home for them?
Ignore the clutter. O___o I never use this, and i've had it since I was about two.

Ignore the clutter. O___o I never use this, and i've had it since I was about two.