I didn't build my teardrop, but it is home built. The builder used sheets of aluminum. He said it's aircraft aluminum. As a gauge, he said it was .068. That might not be right. I've owned it for five years and this is from memory. Have no idea where he bought it.
Here's a bit of cautionary info. He painted that aluminum and apparently did something wrong. I had to use paint remover to rid the top of peeling baby blue paint. And every screw you put in must be protected against leaks. Where he screwed in a plastic doorstopper leaked around the screws. Tnttt.com can help you through their build journals. Good luck on your build and enjoy your travels.