We live in a third floor condo that has concrete planters dividing a continuous back deck between four suites. Our planter is 140cm x 250cm ( 8 feet by 4.5 feet) in area, and 45cm (18 inches) of usable depth after Styrofoam insulating panels are put in. We recently had to remove all plants and soil and sand (there was a lot of sand!) to check for a leak. When we replace we would like advice about depth of soil and amount of sand or gravel to use. There is a drain pipe with holes drilled into it; also, there is an overflow drain at the 40cm level. The two attached pictures show the empty planter as it is now and the planter before the garden was removed. We would like to know how much sand or gravel to put in the bottom on top of the styrofoam panels and how much soil, also what kind of soil mix. The original plants included rose bushes which did not do well against the glass balcony railing last summer, we intend to replace with something less demanding of attention.