My tentative plan down here in the semi-arid central Texas is to use locally sourced (relatively speaking, within 100 miles) quarry block (2' x 2' x 5' limestone blocks) and build thick block walls lego-style. Probably very narrow, so that the roof spans could do earth covered fairly securely. Using pond liners and build above ground. I worry about moisture proofing when below grade. And torrential rains/flooding. But there isn't a single solution, and local climate matters a great deal.
