I saw this on the Daily Dish, http://andrewsullivan.thedailybeast.com/2011/07/roo.html, it is an extremely green roof but a roof that can be simulated in SWMM 5. You simulated it as a Bio Retention Cell with a Surface, Soil, Storage and an Underdrain to the Gutters of the roof. You can also have a rain barrel connected to the gutters to storage and drain the rainfall.
