The most important issue with housing is space. Keep this in mind when you're deciding where
your rabbit is going to live. Of course the best place for your rabbit is inside with you. However this isn't always possible, for
instance, I can't keep my rabbits inside permanently because of asthma, allergies and numbers! To give my rabbits room to move we intially built a condo (pictured) out of a large dog transport crate. A second floor was put in and a ramp. We put a cover over the front of the top floor and with the ramp, this gives them a couple of dark, quiet areas to hang out in. Attached to the condo are two puppy runs, giving them an area approximately 15 feet long and 7 feet wide to run in. We also include a number of boxes for them to hide and dig in. Since then we have moved to smaller groups of buns. All have their own condo's and runs as you can see from the pictures here. The best thing about the cube condo's is the sheer flexibility. You can build up or out depending on space, they're light and easy to move and you can renovate when ever you feel like it.
The same goes for a condo. Make sure there's nothing he can reach that can harm him. Check the for anything sharp, places he could get stuck and anything he can use for a launch pad. Contrary to popular belief, rabbits can jump and climb.
Never leave your rabbit alone outside to play. It takes one second for a neighbour's cat or dog to get into your yard and the results will be traumatic for all involved.
One last note. You may notice a few 'pills' around the place. This isn't a failure in litter training, it's the way rabbits mark their territory, so be prepared.