Pick an area for your warehouse, preferably away from passing traffic, yet close enough to be accessible. Most people consider warehouses eyesores, so balance your need for ease of access against theirs for beauty.
Select the building material: metal, steel, wood or vinyl. Maybe you want to construct your warehouse from odds and ends you have around the house or scavenged material. Remember that the purpose is to protect the items inside from the elements, animals and theft. Use your architectural skills to build a warehouse quickly by using a simple design: four walls, a roof and a large door.
Prepare the foundation area, then examine your materials to make sure you have enough. Among the simplest of warehouse designs is the Quonset hut, essentially a large oval of metal or fiberglass secured in the ground with a wall or doors at each end. These have the virtue of no posts to interrupt the storage space.
Consider buying a steel building that you put together on site. Building from a kit you assemble or a pre-assembled building is your easiest option. American Steel Span and Steel Master USA (see Additional Resources) offer many models of metal storage facilities for home or commercial use.