A greenhouse is classified from glass greenhouses to plastic greenhouses. It is a structure where plants are developed. Sizes vary from small shelters to especially large buildings. Greenhouses are often covered with a range of materials, glass or plastic top and commonly glass or plastic enclosure. Multiplying plants in a controlled environment prevailed in the Roman times. While in the 13th century, Italy put together the earliest contemporary greenhouses as home for exotic plants that explorers obtained from the Tropical locations. These were called botanical gardens. From then on, greenhouses extended throughout the World.