We highly recommend genuine Mexican Beach Pebbles under your outdoor shower floor. Not only do they look nice, but they are excellent for drainage. Available in black and white plus several sizing options.
*Sold per 40 lb. bag
Individual bag covers ~ 2 sf of area layered 2 inches deep. Recommend 3-4 bags for minimum coverage on Standard outdoor showers and 6-9 bags on Deluxe and '83 size without floor.