I use AP T8's with a divider in the middle making 2 24" x 24" x 12" cages. If any of my BP's get too big for their half cage they will get a whole 48" x 24" x 12" cage to themselves. As long as you have secure hides a 48" x 24" 12" cage will be fine for a BP.

The T8 is their cheapest and fastest shipping cage so I highly recommend it. A T8 will be shipped to you within 2 weeks, their other cages can take much longer.