Semi-retired bloke I know built his own several years ago right after pulling the semi-retired lever. He did all the work himself and traded a favor or two here and there so he only had materials costs, fuel for the backhoe, and his own labor. Roughly 20' x 40' x 5' deep. 8" slab for the base, fully grouted block walls, tiled border, flatwork around the top, plastered interior, equipment, etc. Total cost was about 30 grand. I provided one of those favors, so I saw the labor required first hand. It's not for the faint of heart or weak of back. He gets to see the kids and grandkids much more frequently now and is very happy with the $100,000+ still in his bank account.
