Gather the materials. You'll need (in sizes and numbers appropriate to your plans): 5/8-inch or ¾-inch plywood (exterior-grade, commonly called CDX or ACX); 2-by-2s or 2-by-4s; stainless-steel or galvanized screws or galvanized nails; a hammer; a screwdriver or drill; exterior grade caulk; exterior-grade paint (unless you're going to use siding); siding (optional); roofing materials (optional); insulation (sheet polyurethane or fiberglass batts like those you would use in a house).
Step2
Prepare to build the floor of your doghouse on wood or bricks to get it off the ground so that moisture does not wick up through the wood and so that water cannot flow in.
Step3
Build the frame of the floor first to the dimensions drawn in your structural plan. Cover it with plywood. If you're going to insulate, place insulation under the plywood.
Step4
Build the rest of the frame on top of the plywood, making it go straight up from the edge of the floor. Attach the frame to the floor with nails or screws.
Step5
Build the door opening using the same material as the frame. Shape it very simply, like an inverted "U".
Step6
Cover the frame with plywood.
Step7
Build the frame of the roof (See Related eHows), and cover the frame with plywood. Attach the roof to the open-topped doghouse.
Step8
Caulk all seams.
Step9
Add roofing and siding to meet the demands of the weather - and your sense of style.
Step10
Check to make sure no nails, screws or splinters are protruding inside or out.
Tips & Warnings
Be prepared before you begin: Have all your tools and materials at hand. Even a small job can take a long time if you're always running off to the store.
Use screws on at least one wall or the roof so that it is easily removable for cleaning.
Face the opening away from prevailing winds. Also, consider a flap over the door or a commercial doggy-door to slow down drafts.
A bed is necessary in all but the warmest climates - and even there, it's nice.
If you live where it snows, consider a snow fence (a barrier to force the snow into a drift) to keep your doghouse protected.
All materials should be non-pressure-treated; pressure treating is toxic.