Make Magazine interviews Werner Strama, who built his own teardrop camping trailer (here's a detailed HOWTO if you want to try it yourself). Strama talks about how he approached the project and the lessons he learned about scratch-building something ambitious and wonderful:
After we decided on the teardrop, I started collecting hundreds of pictures of all the items we believed would be best for our needs: that is, three person sleeping area, a small kitchen in the back, self-powered when needed, very well insulated, for we would be going camping year round to different places, especially hot springs (we have very nice ones in Colorado). Also I needed to keep the costs down so not to be a burden on our finances, and not to fall into the "credit card trap."
I enrolled my neighbor Denny since he is just an amazing bargain hunter on camping stuff; he was the one who found the old popup camper for free, as well as the stove with the oven, which turned out to be a very nice touch. With the trailer chassis, I set to calculate dimensions and average weights to maintain 12–15% of the total weight on the hitch, which would make sure the trailer would be stable. All it takes is some simple math and three bathroom scales. Then it was a matter of getting the wood, some extra tools, like a router, and a sabre saw to cut the profiles.
How and Why I Built My Own Teardrop Camper Trailer