To build a rabbit cage you can do it the hard way, like this guy is doing:
http://www.youtube.com/watch?v...
Or, you can just build it out of galvanized wire mesh, joined with J-hooks. These are crimping fasteners that will hold two pieces of wire together. Build the size you want -- mine are about 5 ft long and the width of the roll of wire.
After the cage is built, you can rest it on cement blocks -- no need for a wooden frame that might rot, or be chewed by the animal. Rabbits need to be protected from heat and from dogs. The mesh on the bottom should be just big enough for the poops to go through. If their feet go through the mesh, a favorite thing for dogs to do is get under the cage and pull on the rabbits feet. Needless to say this is fun for the dog, but traumatizing for the rabbit.
