Our commercial greenhouses are made of hot galvanized round or rectangle pipes. Under proper use, it can last more than 20 years. Growers can expand the greenhouse by adding new tunnels to the existing greenhouses at the gutter to the existing commercial greenhoses. You can choose any materials as the commercial greenhouses: plasti film, insect net, or shade net as the covering. It is all up to you. Also regarding the ventilation, you can choose the economical manual ventilation, or easy operation auto controlled ventilation. If you are interested in our commercial greenhouses products, welcome to visit: www.greenhousesfamily.com. Or you can contact through the following ways. Email: [email protected] Skype: zoe_greenhouse. AOL: [email protected] Cell number: 0086 13003913916.