The main way in which garage shelving units differ is based on whether they're mounted or freestanding. Mounted units can be attached to a garage wall or ceiling, depending upon the unit's specific configuration. Freestanding units sit on the ground, though some have wheels and can be moved around easily. Garage shelving also differs based on construction material. Many shelving units are metal or wire, but there are also a wide variety of lighter plastic shelving units that fit well in a garage. Some of the actual shelves are made from particle board or MDF. Ultimately, the one you pick will depend upon your preferences regarding weight capacity and the cleaning process. Additionally, garage shelving is available in a wide variety of sizes.