They are an affordable and adequate means of housing rats. When constructed properly, they have adequate ventilation. Climbing space and platforms are not necessary for rats, floorspace is the most important factor, but they can easily be added. Plus, you can make deep bins that allow for tons of bedding to burrow in.

Building a Hammy Loft!

I felt like Snowflake needed a place for digging/burrowing, so I took a plastic shoebox, cut a hole in it, and filled it with bedding. I don't think she likes this bedding, so she didn't seem very interested in it, but I think she'll like it once I get more of the soft stuff she likes. (I bought this at the grocery store when I didn't feel like an extra trip to the pet store... Meh). We're probably going to be moving her into the living room soon; right now she's in Shilo's bedroom, and it's fine because Shilo doesn't sleep in there, but we need to start training her to sleep in her room and a noisy animal might create an issue. We have a TV stand thing in the living room that's attached to the wall, we don't use it anymore because our wall mount doesn't work on our new TV. So I was thinking I'm going to put the Crittertrail on top, medium sized plastic bins on the middle two shelves, and a large bin on the floor underneath. Then I'll connect them with tubes. It should be pretty cheap, and will provide a lot of space and enrichment options. I'm excited about doing this now, and hopefully being in a more used space will help socialize her with the rest of the family (right now she only really plays with me).