If you are looking to install shingles, you might want to consider the closed-cut valley method. It is popular because the two roof planes do not need to be shingled at the same time. In general, the closed cut valley method implies stretching one side of the shingles beyond the valley while those on the other side are trimmed.
The first step is to apply the roofing underlayment. If the two roof planes are at unequal heights, start with the lower roof and stretch the underlayment 36 inches past the valley. Do the same for the upper roof and stretch it 36 inches past the valley. You might want to draw a centerline to help you with correct measurements. If they are at an equal level, it doesn’t matter which side you cover first, of course. The steps of covering one side at a time and stretching it past the center remain the same. Ensure that the underlayment is done perfectly; else you might end up with a leaking roof in the monsoon.
Laying the Shingles
Once the underlayment is complete, it is time for the shingles. Start by laying all shingles on one side of the roofing and stretch it across the valley. Stretch it about 12 inches across the centerline. Fasten the shingles about 6 inches away from the centerline on both sides.
Draw a 2-inch self-stick flashing down the center. Then lay the shingles on the other side of the roof and again stretch them across the valley a little. No need for precise measurement. You have to cut the shingles back to 1 inch from the centerline. This layering will help direct the water into the valley and down the roof, preventing leaks.
You might want to consider working with architectural shingles. For starters, they are not as expensive compared to standard three-tab shingles as you might make them out to be. The price difference is overcome by the aesthetic appeal it gives to your roof. Also, they last longer and can weather any hailstorm. And yes, they are easier to maintain.
A Couple of Tips
Try to put a metal sheet between the two layers of shingles. This will help protect the lower layer while you are cutting the shingles from the upper layer. Also, when cutting, do it patiently and cut one shingle at a time.
Closed cut valleys are notorious for their ugly looks. Indeed, the overlapping shingles make the roof look very unsightly. Further, they wear out faster than a metal valley. This might lead to annoying leaks in heavy rains or at the very least a damaged roof underlayment.
These disadvantages are neutralized by their simplicity of installation.
Alternatives for the closed cut valley installation are the woven, metal, open cut and long island installation. All of these have their own pros and cons and you might want to look them up before you start installing shingles.