Putting a roof on your dog's pen will keep the cold wet weather off of him as well as provide a shady place to snooze when summer temperatures soar. You might choose to roof the entire pen, or you could roof just part of the pen, so that Rufus can decide on his own whether to sit in the sunshine or seek shelter. Even though you'll use exterior grade plywood, it's still wise to weatherproof the roof of the dog pen further. You could apply shingles to the top of the roof, but covering it with a tarp is less labor-intensive.
Determine the measurements for the roof. For example, if your dog's pen is 8-by-6 feet and you want to roof half of that measurement, the roof will be 4-by-6 feet.
Measure out 4 feet on the 2-by-4 using the tape measure and mark it with the pencil.
Cut the 2-by-4 with the saw along the point you marked.
Saw two pieces that each are 6 1/2 feet long from the leftover piece of 2-by-4.
Lay the two 6 1/2-foot pieces of 2-by-4 across the top of the pen, spaced 4 feet apart. In the example, the pen is 6 feet wide, so the 2-by-4's will extend over each side by 3 inches. These pieces of wood should be laying flat.
Position the 4-foot piece of 2-by-4 across the ends of the other two pieces on one side of the pen. Lay it so that it stands tall rather than laying flat.
Secure the 4-foot piece of 2-by-4 to the other pieces using the drill to drive the screws through at an angle. You'll use 4 screws total for this step: 1 each from the front of the 4-foot piece down into the 6 1/2-foot pieces, and 1 each from the bottom of the 6 1/2-foot pieces up into the 4-foot piece. Place the bottom screws 1/2 inch apart from the top screws so that they don't meet in the middle of the wood.
Measure the plywood to the correct size using the tape measure and the pencil to mark off a 4-by-7-foot square section, then cut it with the saw.
Lay the plywood over the pen on top of the 2-by-4's. It will meet the 2-by-4's evenly on the 4-foot sides, but it's longer than the pen's 6 foot width, so it will extend 6 inches beyond the front and back portions of the pen to form eaves. You'll also see that the roof slopes down in the back to allow for rain or snow to run off.
Secure the plywood in place using the drill and screws to attach it to the 2-by-4's at all four corners. You only need one screw in each of the four corners, but use three or four additional screws along the front edge to attach it extra securely, depending on how long your roof is. In this 4-foot example, you could use 3 additional screws spaced approximately 1 foot apart to ensure the front part of the roof is fastened firmly in place.
Position the tarp over the roof and affix it to the plywood using the staple gun.