Currently my two share a puppy exercise pen that is 4'x4'. It's not nearly big enough for two bunnies (one of them is very active), in my opinion, but it's temporary as they stabilize their bond.
Their permanent set up (which was my original bun's set up) is a 4'x2' Superpet Giant cage (so one of the plastic bottomed cages) with the xpen attached to make a run. The total set up is 4'x8' I think. I could get another xpen and ditch the cage, but I actually like it as I can keep all of their hay in there and it's easy to clean. When they have hay in the pen, they spread it all over and it ends up leaking out throughout the house, causing allergy problems for my husband.
The flooring on the petstore cage is plastic, but I put down pieces of fleece as one of my buns likes the extra traction (the other bun doesn't mind the plastic bottom). I just bought fleece at a fabric store and cut it to fit. I can take them out and wash them as needed. The floor of the pen is a tablecloth protector. Basically a piece of vinyl with a felt backing meant to protect dining room tables under a decorative table cloth. It's not good for super diggy or destructive bunnies, but it has worked for us so far. If our new bun decides to destroy it, we'll probably get chloroplast.
Both bunnies are litter trained. Our new female has marked a bit when she's put into a new cage/situation, but the table cloth thing is easy to clean up and after a few days she uses the litter box exclusively.
