Things You'll Need
4-foot by 8-foot plywood sheets
Draw a plan for your structure. Measuring your pallets before you design your structure will help you plan the size of your structure. You can plan according to your pallet sizes to keep the required cutting of pallets to a minimum, and possibly plan your doors and windows so that you don't have to cut them out later.
Pull apart some of the pallets. This will provide you with two-by-fours to use for attaching the whole pallets to each other and filling in holes. Nail two-by-fours into the open ends of each pallet, so that you have a solid frame around each pallet.
Build the floor of your structure. Attach the pallets to four-foot by eight-foot plywood sheets to get the floor size you desire. If you want an eight-foot by 12-foot flooring surface, for instance, you can lay two boards side by side and a third board lengthwise at the bottom. When deciding on the size of the floor, keep in mind it will be easier to cut down the plywood sheets than it will be to cut down the pallets. Attach more pieces of plywood to the other side of the pallets to create a solid floor.
Stack pallets to craft the walls. You can cut down pallets with a saw if necessary. Pallets should be bolted together for maximum support. Lightweight pallets work better for walls. Build one wall two to three inches shorter than the one across from it, and build the two adjacent walls so that they slope down from one wall to the other. This will give you a simple sloped roof that allows water to run off.
Build your doors and windows. If you have planned your structure with door and windows built in, it will save you some trouble at this point. If you haven't, you can cut out the windows and doors with a saw. Reinforce the windows and doors with the two-by-fours you have pulled from the pallets. Nail the two-by-fours into place.
Put on your roof. Nail enough pallets together to stretch between your walls. Nail plywood to the top and bottom of the pallets to create a sturdy ceiling and roof support. Your roof support should be slightly larger than the rest of your structure and can be nailed on top. You can put shingles or roll roofing on top of the plywood just as you would any other roof.
Line your walls and put in doors and windows. Now, just line your house with plywood on the inside and outside. Waterproof exterior wood with a sealant. Attach a pre-built door and pre-built windows to complete your structure.