This is Boris. Nice to hear that you are trying to move out! I could send you a dvd: Primitive Semi-Permanent Shelters by the mcphersons ( http://www.amazon.com/Primitive-Semi-Permanent-Shelters-John-McPherson/dp/B000EE26DQ )
Or you could ask Ran Prieur, who is building a wooden cabin. In this FAQ he states "
I read all personal emails and answer most. I like answering questions.". So chances are good
In his landbase FAQ disencourages to built an underground house:
"Have you looked at Mike Oehler's $50 and Up Underground House Book?
Yes. Here's a link to Oehler's underground housing site, and I also cover this in the September - October 2004 archive. Oehler's book was the first thing I bought after I got the land. Then I did more research and found out that his PSP method is risky and very likely to leak. Everybody wants to live in a "hobbit house," but if Bag End were real, it would have water running out the walls six months a year without sophisticated waterproofing. Also, a U-house is not breathable -- to be fair, neither are "normal" houses. Also, as Oehler admits, a U-house requires a lot of digging, and wet soil is a terrible insulator -- the only advantage is that in the winter the stuff behind the wall is only 20 degrees colder than the inside instead of 50 degrees colder. Some people make underground houses work, but on the whole I prefer cob or cordwood."
By the way, I am going to travel southwards, to Malaga in october and stay there for a few month. When I am back, I would glad to see you! Unless you decide to build your house in Spain, then we can meet ealier.