You should look into the regulations where you'll be going before building a shelter. Here in the Ozarks I know there are places where you could get fined for doing that.

Having said that, I have run across a few shelters that I thought were pretty darn cool. Like phat said, they wouldn't keep you very dry but they were still very creative in design and fun to play in wink

I might make one on our property one of these days myself. My grandson is about 2-1/2 and it'd be fun to build one with him.