Rather than start a new thread, I thought I'd jump into this one, since so much has already been said here.
I'm probably building something based around the $50 underground house. Before I put so much work into digging that I can't change my mind, I have some concerns/questions. (I do at least know from the well drillers that I probably won't hit a rock shelf unless I go down 100 feet!)
From what I've gathered here, pond liner is now recommended for the roofing, the roofing material should also be extended a good distance away from the sides, french drains are recommended around the perimeter, and it is no longer recommended to set the posts into the ground.
Questions concerning my situation: I'm located in north central Arkansas. The hillside I have available is west-facing. Does this present any unique problems I may not be considering? Mike's book seemed to recommend south facing slopes, but I do not have one available. The housing site I selected is roughly half-way down the hill, but probably closer to the top than the bottom.
Is pond liner also recommended for the sides, or is it really only needed for the roof?
Is there a problem with using oak/hickory for the posts, beams and girders? I have a lot of it available for free, so I'd prefer to use it unless there are good reasons not to.