You must cut roof shingles before affixing them to the roof in order to keep gaps from lining up, allowing water to pass between and under them. To prevent a leaky roof, make cuts using a paper cutter or scissors.
Stagger Cuts to Create a Pattern
Cut a section of 6, 12 and 18-inch shingles. Most tiles have guide marks that can be followed to make cutting easier. Be careful not to deviate from the lines too much as this will create an awkward pattern when attaching the shingle.
A paper cutter specially designed for use on roof shingles can be rented from an equipment rental store or a home improvement center. This will help keep your cuts uniform and help you maintain the pattern.
Cutting Around Pipes
Shingles are typically pre-cut or notched to fit around pipes. Use a utility knife to make a circular cutout to fit the shingle around the pipe. Measure the area that the shingle will be fitted around with a tape measure to make sure that it fits properly. Mark the cut area with a pencil and make the cut.