"people in albany and new york city are using “green roofs” to improve the environment. a green roof can be added to many buildings that have large, flat roofs. green roofs have three parts: a protective layer to separate plant roots from the roof of the building, an absorptive layer to catch and hold rainwater, and a layer of plants. often, green roofs use sedum, a short, desert plant, because it is efficient at storing water in its leaves and can withstand the colder climate.
a green roof saves energy, reduces carbon dioxide in the atmosphere, and prevents rainwater and melting snow from overloading sewer systems. it can also protect the roof of a building from damage. however, green roofs can be expensive to install, and require care and maintenance.
state one disadvantage of a green roof."