My project features raised green roof beds (6" deep soil) located directly downstream from a tin roof. There are no gutters and for the most part runoff from the roof runs directly into the roof beds, the excess runoff from the green roof then runs into an order flat roof where it is directed to standard storm drain. My project also has a roof terrace surrounded on the perimeter by green roof bed as well. The roof terrace rain scuppers are located in the green beds, thus the runoff from the flat terrace must pass through as well. For the purpose of calculating my BMP area for capture, storage, and treatment, can I consider the sloped roof as an addition to my 1st green roof bed, and the roof terrace as addition to my 2nd bed? The EPA National stormwater Calculator doesn't have a capture ratio for green roofs, although it does have a capture ratio for rain planters. But the rain planter model requires a permeable surface beneath something I don't have.