Green roofs cost more to build than regular roofs, but in the long term, they allow building owners to save money. In most cities, people have to use air conditioning to stay comfortable in the summer Building owners pay huge electricity bills to run that air conditioning. With a green roof, much less air conditioning is needed. Studies have shown that a regular black roof can reach 180" F(82 C) on a summer day, while a plant-covered roof will stay much cooler, not more than 85"F (30"C). This makes a big difference in the temperature inside the building