If you are interested in heavier plants and heavy growth, you need to understand that this will be an intensive roof that is able to handle 30 pounds or more within a single square foot. However, there are still limitations in regard to what you can grow on a roof, so you should express your ideas and concerns to professionals that deal in the industry of constructing green roofs. For homeowners that are looking to grow lightweight plants, an extensive roof may be all that is necessary for their green roof, which means every square foot can withstand a weight of 18 to 22 pounds.