Had to do it twice, once for a 15' Intex then for my FantaSea. The SE end is on the ground and the NW end is elevated almost 3 feet! Had to use retaining wall block and fill it with Quarry Product--like crushed stone only not as clean, but just as much drainage and higher coefficient of friction. Cost a painful fortune (few AG pools cost as much as that base!) but well worth it.