There are many designs out there for underground homes and semi-bermed homes.

I just saw, in Oklahoma, where this family has taken an old steel tank (5,000 gals???), turned it on its side, cut in a doorway, and has buried it as a tornado shelter. It looked like it could hold between 10 and 20 persons comfortably. It is buried into the bluff created by the roadway being cut through a hill and they are facing the sides of the bluff with natural stone, on each side of the shelter entrance.

Yes, I've been on the road for the last five days but that is another nightmare,,,uh, I mean,,,,,another story!!!!!