I've read that, to be comfortable, an 8x4 is good. I don't have an 8x4 wall to give up, but I do have a 6x6 enclosure. Look at this illustration and try not to laugh 
http://s666.photobucket.com/albums/vv29/MangaFreak1/?action=view¤t=cage.jpg
See, the bottom layer is the substrate she can burrow in and such, which would be about 2-2 and a half feet deep (giving her a leather box and such should limit her need to burrow down deep, right?) That leaves about a foot of room before before the top part. It's the same width, but shorter to provide room for the stairs. It'd be a different design/layout, but the concept is the same. She climbs up if she wants, there's about 5-6 inches of substrate or more if needed. The light and such can go up there, so up on the second layer is her warm area and down beneath is her cool area? I also added in the corner a little thing on the side for extra shade -just in case. Also, as you can see, it would be level with the windows. If that's a problem I can block them out, but otherwise seems like extra warmth from the sun and something to look at..
That's the first draft of the idea. Please give be objections/changes/ and such?
btw, the "666" is purely a coincidence, and I didn't choose them. Someone had to get them and I guess it was just my lucky day (sarcasm). Sorry if it offends
http://s666.photobucket.com/albums/vv29/MangaFreak1/?action=view¤t=cage.jpg
See, the bottom layer is the substrate she can burrow in and such, which would be about 2-2 and a half feet deep (giving her a leather box and such should limit her need to burrow down deep, right?) That leaves about a foot of room before before the top part. It's the same width, but shorter to provide room for the stairs. It'd be a different design/layout, but the concept is the same. She climbs up if she wants, there's about 5-6 inches of substrate or more if needed. The light and such can go up there, so up on the second layer is her warm area and down beneath is her cool area? I also added in the corner a little thing on the side for extra shade -just in case. Also, as you can see, it would be level with the windows. If that's a problem I can block them out, but otherwise seems like extra warmth from the sun and something to look at..
That's the first draft of the idea. Please give be objections/changes/ and such?
btw, the "666" is purely a coincidence, and I didn't choose them. Someone had to get them and I guess it was just my lucky day (sarcasm). Sorry if it offends