I dug hole 12x10 . Poured 6” floor concrete with rebar . 12” blocks for walls 8ft tall . Built form for top was hardest thing. Lots bracing under bottom before pour . Pour the walls full concrete and 10” on top with lots rebar . Put a pvc pipe in center of roof for some vent . . Drain in floor also . I built a huge thick door out of wood that opens to the inside . I need get a fema approve metal door a get the shelter approved by them an i get cost off state taxes . Bout 4k total cost but it was friends a family deal on the block laying a concrete . It’s bout $ 150 a yard here . I put mine up aganist any tornado . I also seal the outside before I covered it up an put drain around bottom on sides