I don't think one Billy cage on its own meets the minimum requirements, so people tend to put 2 together (
https://www.youtube.com/watch?v=iDg1mWT0q90&t=91s). You can also put 4 together as seen on ErinsAnimals Youtube video (
https://www.youtube.com/watch?v=nGLN4N_lGRY) to make an even bigger cage. I've not got one, but am considering making one as I think they look fab!
