The Quonset type buildings work good. We had several at work which was corrugated steel and was buried. They had been used as ammunition bunkers during WWII. The only thing wrong was water from the shallow water table, other than that they were great.

I am going to look into these things and find out what the load rating is to see if then could be covered just a little more... Just a thought, they could also be great covered in chicken wire and sprayed with concrete mixed with fiberglass. I like that idea and then the foam insulation. The only thing I think I would spray on the insulation to the outside and keep the living area the way it is, that way I would have more space, just concrete over it.