Have you ever thought of a garden on a roof? It is actually good the environment and people. The roof of building can get extremely hot during the day. Therefore green rooftops can actually cool the air in the cities. A single green roof will not do to change the temperature of a city. However, more buildings begin to convert their rooftops to green spaces, a real difference can occur. Buildings are cooler will use air conditioning less often. reduces the amount of energy a building uses, which is good for the environment. Plants on rooftops can also help clean the air. Having a large number of plants in an area creates breathable air. Some people feel that green rooftops can be more expensive traditional ones. The roof has to be flat and strong enough to support the weight of the garden. Rooftop gardens can also dry out quickly the hot season and vegetables need frequent watering. These difficulties discourage building owners from investing in rooftop gardens. However, the benefits have slowly outweighed the limitations.