what materials can you use to cover roof valleys
Where valleys run from the edge of the roof to a ridge, trim the flashing to fit under the corresponding side of the ridge shingles. Pull the nails at that side of the ridge shingles to install the flashing, and re-nail the ridge after the flashing is nailed in place.
If the distance from the roof to the ground is 20ft., then you would need to use 40ft. of rope for each corner of your home. The most popular item used to cover a roof is a tarp. These are very inexpensive and can be found in the home improvement section at almost any department store.