A simple wooden doghouse doesn't have to be a time-consuming project. You can build one in a day or over a weekend. You can make one that's simple, or finish it with some trim to add some flair. A simple square doghouse of 36 inches would be large enough for most dogs.
Cut four 2-by-4s to 33 inches in length. Cut two more 2-by-4s to 36 inches. The long boards are the sides of the doghouse;s floor frame, and the short boards are the floor joists.
Drill two pilot holes into each end of each joists, to keep the wood from splitting, and space them 10 inches apart, parallel. Sandwich them with the 36-inch 2-by-4s, perpendicularly, to form a square. With wood screws, drill through the 36-inch boards and into the pilot holes at the ends of the 33-inch boards to fasten the floor base together.
Use a circular saw to cut a piece of 1/2-inch-thick plywood to 36 by 36 inches, just large enough to cover the floor joists completely. Attach the plywood floor with 22 2-inch-long wood screws, spaced out every few inches, all the way around the edges of the floor. Make sure the corners are square so everything fits perfectly.
Cut six 22-inch-long 2-by-4s and four 36-inch-long 2-by-4s to frame two side walls of the doghouse. You'll use three 22-inch-long pieces and two 36-inch pieces for each wall. Drill two holes into both ends of each 22-inch upright. Place two 22-inch boards so their outer edges are 36 inches apart; center the third 22-inch board between them. Sandwich them with two 36-inch-long boards, and fasten them together with 3-inch wood screws, screwing through the 36-inch-long boards into the 22-inch boards' pilot holes. Do the same with the other set of boards. Then screw the completed wall frames into the side edges of the floor using 3-inch screws set a few inches apart.
Build the back wall frame the same way as the side walls, using two 22-inch boards and two 33-inch boards. Screw it to the floor panel.
Cut two more 33-inch-long 2-by-4s and four more 22 inch ones for the front wall frame. Cut one 2-by-4 to 8.5 inches to frame the top of the doghouse door. Drill pilot holes into the ends of the 22-inch boards, sandwich the four 22-inch boards between the two 33-inch-long boards at 8 1/2 inch intervals, and secure them by screwing through the 33-inch boards into the 22-inch boards' pilot holes. Screw the 8 1/2 inch piece of wood 18 inches from the bottom, in between the two center risers.
Cut the 5/8-inch-thick plywood sheet into two 29-inch-by-36-inch rectangles with a circular saw. Nail these two pieces of siding into the side wall frames using 1¼-inch nails. Cut the lower back panel to the same specs as the side panels but with a pointed top 4 inches taller than than the walls, or 26 inches. Cut the front panel to the same dimensions. Then cut out a 10-inch-by-15-inch door using a fine blade in a jigsaw. Nail the front and rear panels to the edges of the wall frames using nails spaced a few inches apart.
Cut eight 29-inch 2-by-4s to frame the roof. Cut a notch 3½ inches from the bottom edge of each board. The notches will allow the roof frame to rest on the side walls. Drill a pilot hole at the point of each notch where the boards will attach to the walls. Cut a 2-by-4 to 36 inches and screw that into the tops of each of the boards in the triangle-shaped roof frame with 3-inch-long wood screws at 10-inch intervals between the upright boards.
Cut two sheets of 1/2-inch plywood, making sure that one of them is 37¼ inches by 30½ inches and the other sheet is 31 inches by 37½ inches. By cutting one longer than the other, you'll allow the longer sheet to cover the top end of the shorter one. Use 1½-inch screws placed 10 inches apart to fasten the plywood sheets to the rafters and to the top beam of the roof frame.
Staple tar paper into place on the roof, making sure the tar paper is cut to the exact size of the roof. If you want shingles, install them beginning with the bottom left section of the roof, using roofing nails.