Storage-Buildings.com considers any storage buildings over 200 SF to be "buildings" rather than just sheds. As mentioned above many city and county building departments will require a building plan submittal and inspections when you build and install a building over 200 SF. This typically also means that you will have to be a licensed contractor (Class A or Class B) and that you will have to have a proper foundation for the building that has been designed by a licensed, professional engineer.
Wood buildings are typically made from 2x lumber, plywood, roofing, and siding. Wood buildings range from a custom shed built to meet your needs all the way to a pre-built building that can be delivered to your site. Wood buildings are known to be strong and durable (when built well) and they can be known to last a long time as well as they are kept waterproof with proper roofing and siding as well as kept in good shape. Some weaknesses of wood buildings are that they are subject to termites and moisture problems such as rotting or mold issues when there is not "proper drainage" around the building.
Metal buildings are typically made of a steel structure and metal sheeting. They are known for being both durable and sturdy, however, it depends on the brand of the building and/or the thickness of the structural steel members and the gauge of the metal sheathing. Although they are known to be durable metal buildings may be prone to rusting under wet conditions especially if any of the metal is not galvanized or stainless steel.
Plastic buildings are known to be practically maintenance free. They are not prone to moisture, mold, or rust issues and the plastic that they are typically made of can be cleaned pretty easily. The major limitations of plastic building is the overall strength. Since plastic is not as strong as either metal or wood they are typically limited in size and have a difficult time meeting any building codes without the addition of metal structural members. Sometimes a combination of plastic and metal (such as vinyl coated steel sheds) can bring the ultimate combination of strength and durability.