The first decision is whether to simply patch leaks and damaged areas or whether partial or complete reroofing is in order. If you choose the latter, you’ll also have to decide whether to roof over your existing roof or whether to remove it. There are cost consequences either way.
Replacing shingles due to wind damage or a fallen limb is a relatively easy and inexpensive. Torn or damaged shingles can be removed, and new ones can be slipped in place. The downside is that unless your roof is relatively new and you happen to have saved some spare shingles from the job, your patch job may not match the existing roof. But that is a small price to pay if the repair would extend the life of your current roof for another 10 or 15 years! However, if you plan to sell your home in the next few years, ask your contractor to order shingles that match as closely as possible. A roof with a prominent patch is unattractive and will not inspire a potential buyer’s confidence.