Urban areas create several environmental problems. A major problem discussed widely now is the urban heat bubble. Asphalt on roads, parking lots, and roofs reflect heat into the air. This causes a heat problem. Other issues involve water. The asphalt and concrete that make up our urban areas do not absorb the water, so we get flash flood effects in our storm drains and sewer systems. Another problem is air pollution. Not only do we clear land full of oxygen producing plants, but we put carbon dioxides in the air.
These are all issues that green roofs can help solve:
reduce ambient air temperature, energy use, and utility costs
help cleanse the air and water
utilize local and recycled materials
extend the life of the roof
create green space for humans and wildlife while providing a psychological and physical respite from urban surroundings (Velazquez)
Green roofs are generally intended for flat commercial roofs. The weight is greatly increases and the roof should be engineered accordingly. Residential roofs can potentially support a green roof system. I suggest looking into a modular system. Do your homework before installing any kind of green roof system. Plants should be selected to withstand a windy and hot climate. Drought and cold resistance is also a good idea for most of the United States and Canada.