A rabbit needs at least a 24″ by 48″ cage, that is high enough so their ears do not touch the top when they stand on rears. There should be a door that can be opened so they they can come and go as the please (you just can’t keep them caged all the time). They need a private, dark space.
What I put together, is all that and it has an extra door on top (think cleaning), removable litter pan and you can build it your self.
Follow the link to see how it was done.