Joanna, “Standing Seam Metal” roof material systems are considered to be the best choice for builders and architects that are attempting to meet federal efficiency standards for building green. This product is often made from recyclable materials. This type of roof system has a much longer life, 50+ years when installed correctly. This roof material also has a high reflectivity index depending on the color selected. Metal roofing can also provide relatively clean water for a collection system that may be present. Other green options would include tile roofing with venting under tiles, flat roofs with white coating, vegetation roofs and specialty colored shingles designed for higher reflectivity.