Well originally I was going to do 18x12x30 but I thought 30in was too high for her right now so I figured a little smaller might be better for a couple months. The reason it's so narrow is so it will fit on the shelf in the corner of the room which is about the only place I can put it until I rearrange the room and/or buy a wider shelf. That shelf needs to be that small so I can open my closet door but the cage doesn't have to stay there if I find something to sit it on. This was going to be a temp cage for a month or 2 while I build a slightly bigger/nicer one and seal it and everything. If my original dimensions work, I can just go with that. The wood is cut for 18x12x30. Eventually she'll have a 2x2x4 cage for when she's full grown.
So should I keep 18x12x30? If so, how long would that size last before she needs her adult cage? Or should I build an in-between sized cage?