Am doing my thesis and my topic concerns using digitalglobe images to identify roofs and compute their areas. I want to use this information to try and estimate the amount of rainfall that can be harvested from rooftops in Mombasa City, Kenya. I am trying to digitize the roofs manually in arcmap but the process is tidious and time consuming. I also tried the image classification tool but the results were not that impressive. How best can I extract roof areas from the raster data (images). I am working with three roof materials: Concrete, tiles and iron/steel. Any idea?