. . "20x20 5000 ft 2 250 ft 2 10x25, 13x20, 500 ft 2 20x25 15x17Source: North Carolina State University Cooperative Extension; reprinted with permission.*Roof, driveway, or other surface that serves as a source of runoff.Constructing the GardenUse a string, rope or hose to outline the footprint of your garden." . .