Hunter, I couldn't begin to tell you how to make one, but we just bought a truck box and 8 dog houses from Crossroads Hobby Shop in Russell Springs, KY. They are very lightweight insulated aluminum and the quality is unmatched for the money. We bought a huge truck box, 48" x 44" with storage in the top, and other than being awkward, it would be a one-man lift. His prices are very reasonable. A fellow beagler on this board referred us to him.
If you decide to buy instead of build, call Bobby Guffey at Crossroads Hobby Shop, 270-866-5262, or watch for his upcoming ad in The American Beagler. He will build to your specs. (he even makes the sports boxes that go on the back of an ATV).