Step 1
Examine the space under your home. Your goal is to design a room that has walls no closer than six feet from a home's foundational footings. Digging close to the foundation can damage it. Make the room's length and width at least eight feet by eight feet, if possible. Try to make the room at least six feet in height.
Step 2
Dig and build steps from an exterior crawl space door that leads down to where your room will be. Since your crawl space is probably only three to five feet in depth, make the new storage room approximately six feet tall. Because most crawl space areas are not waterproofed like a basement, digging any deeper might allow water to seep into the space.
Step 3
Dig out all the dirt before beginning work on the room. Install wooden framework and pour a concrete slab floor. Roll out metal grid work to strengthen the concrete flooring. Build a room of cinder blocks and nail a ceiling in place by installing plywood to the floor joists. Use boards and plywood to cap around the top perimeter of the room. Watch for pipes and wiring that might be in the way. Make sure the room has wiring for an overhead light and wall switch.
Step 4
Brush waterproofing on the inside of the room. Install a wooden or metal door jamb and a lintel beam over the door and threshold. Attach a metal or wooden door with hinges. Install a deadbolt lock, if desired. Place metal shelves in the room to hold supplies, food items or tools. Avoid nailing directly into cinder blocks or concrete when installing shelving.