If your snakes are going to be sharing the cage just for the breeding season, it shouldn't need to be too large. I would think that a 36" x 24" x 12" cage should be fine if you are planning on housing them separately after the breeding season. The three foot cage wouldn't be too large for a single adult female to live in. A lot of cage manufacturers make this size cage if you ever think about purchasing one online. Here's just one of them: http://www.reptilebasics.com/2x3-Cag...h-p-16286.html