This doghouse is suitable for a small to medium-sized dog with a 9 square foot base. I purchased my materials at Home Depot. Note that the doghouse uses an existing floor--in my case, an outdoor deck--so no base is included in this plan. If you need a base, purchase additional materials as required.
Tools needed: hammer or cordless drill, table saw, circular saw, jigsaw, tin snips, small paintbrush
1 sm. box approx. 1-1/2 roofing nails
1 sm. box approx. 2 1/2" galvanized common nails or screws
1 sm. box approx. 2" galvanized finishing nails
1 pack of asphalt/fiberglass shingles
2 10' sections of 2" drip cap
1 quart exterior paint
2 sheets 7/16" OSB (oriented strand board)
1 sheet blue insulating foamboard
Step 1: Mark and Cutout Parts
Make a sandwich with the two OSB sheets on the outside and the foamboard inside. Make sure that the edges line up, then fasten the sheets together with 4 nails or screws to prevent shifting. Draw the parts on the top sheet as in the first drawing below. Then nail/screw additional fasteners about every foot just inside the edge of each part to be cut. This will hold the parts together when they are cut. Cut the parts out using the circular saw. Use the sabre saw to cut the corners of the door opening. Cut two equilateral triangles 10" on a side from the door opening scrap. Attach the two right-triangle sections to make the back wall. (I nailed 1x2's to the top and bottom inside edges to hold them together.) For the ridge, carefully cut the 2x4 4' long and 2 5/8" wide. Then use the table saw set at 30 deg. to rip this piece into a diamond shape (see 2nd drawing).
Step 2: Assemble Wood Parts and Paint
Draw lines at 3" and 4 1/2" from one small end of a 3'x4' roof section. This will be the attachment point for the back wall. Turn the side over and repeat this marking on the other side. Draw lines at 9" and 10 1/2" from the other small end of the 3'x4' side. This will be the attachment point for the front wall. Turn the side over and repeat this on the other side. Mark the other roof section exactly as indicated above. Line up the base of the front and back walls with the marked lines of each roof section. Note that the top inside edges of the roof sections should just touch each other. Screw or nail the sides to the bottom with the 2 1/2" fasteners. Attach the ridge piece to the tops of the left and right roof sections with the 1 1/2" and/or 2 1/2" fasteners. Line the door opening with 1 1/2" wide scrap pieces. Fasten the triangle vent covers on each end backed up by the scrap from the ridge piece using the 1 1/2" fasteners. Paint front and back walls and undersides of roof sections that will be exposed to the weather with 2 coats exterior paint.
Step 3: Attach End-cap and Shingles
Attach drip-cap along all edges of the roof with roofing nails. Make a starter coarse of shingles along the bottom of one side of the roof attaching it with roofing nails, then lay the first course of shingles directly over it. the nails should be placed along the tar section of each row and above each tab. Trim shingle material that hangs over the drip-cap. Start the next row of shingles with the tab staggered half-way between the first shingle tabs. Line up the base of the second row of tabs with the top of the tabs on the first row. Repeat this until you get to the top of the roof section. Trim the extra material off. Repeat shingle installation for the other roof section. For the ridge cap, take leftover shingles and cut the tab sections off and attach them on the ridge perpendicular to the ridge line. Overlap them so that the tar strip is just covered. The last shingle will have two nails visible.
Step 4: Optional -- Floor
To add a floor, cut a 3'x3' section of plywood or OSB sandwich and attach it to the bottom of the roof and front/back wall sections.