Determine the width of area you want to cover. Square your outer wall with your existing wall. To do this, measure out on both ends of your existing carport to the length you desire. Set your two outer posts. Now you may build your beam or wall to run parallel with your existing carport.
Continue your project to extend the roof on an existing carport by determining what type of roof you want to build. For this example, we are building a shed roof off of the existing carport roof. A shed roof is simply a straight roof on an angle.
Figure the height of your shed roof. If you build your beam the same height as your existing beam on your carport, you must raise your rafters up on your existing roof so you have fall on the opposite end for weather purposes. Too little fall prevents water from running off of your roof system when you extend the roof on an existing carport.
Cut your rafters to extend the roof on an existing carport. It's best to install your roof rafters on 16-inch centers. This makes your roof sturdy. After all rafters are cut and nailed in place, put ½-inch decking plywood on your rafters. Felt your decking and get ready to apply shingles.
Start shingling on the low end of your roof, working up to the top of the existing roof. When you reach the top of your existing roof, you must raise the shingles of the old roof and slide the new shingles under them to prevent leakage.