Rabbits are popular pets and easily can be litter trained to be just as house friendly as cats. But they can't run free in your house all the time; a rabbit needs a cage to live in when you're not supervising his romps.
You can buy a rabbit cage, but they're usually either very small or very expensive. Luckily, it's pretty easy to build your own rabbit cage, and rabbit breeders do it all the time. The question is, do you want to house your rabbit outdoors, indoors, or both?
The Indoor Cage
It's best to make an indoor rabbit cage entirely from metal because it's easier to clean and keep sanitary than wood, and it's quite simple to put together.
Your material will be galvanised wire; use a 1" x 1" mesh in 14 gauge weight for most of the cage except the bottom, which should be 1" x ½" mesh. Fourteen gauge is fine for the floor, but you can also go to a heavier 16 gauge if you want it a little sturdier. Then you need wire cutters to snip the wire, 3/8" hog rings to hold the pieces together, and hog ring pliers to clamp them in place.
Make all the sides of your cage in one long piece by folding it three times into a rectangle; a good size is 30" deep and 36" wide, so you'll be folding your galvanised mesh at 36", then at another 30", then at another 36". You can do this easily by just measuring and bending the mesh over the edge of a table. Then you just need to attach a 36" x 30" roof in 1" x 1" mesh and the same size floor in 1" x ½" mesh.
To make a door, you simply cut a piece out of the long side of the cage, about 2" from each of three edges (top, bottom, and one side) and about 12" wide. Then cut another piece of wire mesh that's an inch bigger than your hole on all sides and attach it to the cage with hog rings as hinges; the side where your door hole is 2" from the edge will be the side you put a latch on, which you can either make yourself out of wire or purchase.
On the far side of the door, consider cutting a hole for an automatic feeder to go through; this allows you to pour food in the top, and it collects in a little dish inside the cage.
Somewhere on the inside, you'll also want to put a hay rack, which you can make out of a rectangular piece of wire mesh about 8-12" wide and attach to the cage with hog clips. Mount it at a 45 degree angle with the opening at the top, and bend the sides in; this is perfect for holding a few handfuls of alfalfa or timothy hay, which your rabbit can eat through the mesh holes. Don't forget to put a water bottle on the front or one of the sides, with a sipper tube for the rabbit to drink from.
The Outdoor Hutch
If your rabbit's going to spend time outdoors, you should make a wooden hutch to protect him from the elements. The front and bottom can still be mesh, but the sides, back, and slanted roof will be wood, and the whole thing should stand on wooden legs so predators can't get at him.
The legs should be about 24" tall and the hutch another 24" tall on top of that. Use 2x2s on the four corners as both the legs and the corner pieces to the cage; use more 2x2s around the perimeter of the floor. Brace the legs with pieces of 1x2 set on a 45 degree angle from each leg to the bottom perimeter of the cage. A good depth for the cage is 24", too, but it should be about 96" wide so there's lots of room for your rabbit to run.
For the wooden sides, back, and roof, use 1" x 6" boards placed horizontally for the best durability. The back of the hutch should be slightly higher than the front so that your roof is at an angle slanting forwards, and rain won't collect on top.
On the bottom of the hutch, use the same 1" x ½" galvanised wire mesh as for the indoor cage; this allows the rabbit droppings to fall right through to the ground, and you can collect them to use in composting. Attach the mesh to the wooden floor frame with a staple gun.
For the front, double doors will make it easier to access all areas of the inside. Use a 2x4 in the middle to support the two doors and hold the latches. Use 2x2s to create frames for the doors that will fit snugly within the frame of the hutch front and two more 2x2s at the outside edges of the doors to attach the hinges to. The doors and the rest of the hutch front will be the same 1" x 1" wire mesh as used on the indoor cage, and that can be attached to the wooden frames with a staple gun.
If you need bigger or smaller cages or hutches, you can adapt the measurements, but most homemade rabbit houses use a variation on one of these two themes.