Reading a repair estimate
If you have collected a few estimates, look for whether each one says what is actually wrong and where. A good repair scope names the failure point, the material to be used, and what happens to the surrounding area. A vague line that just says roof repair tells you nothing and is usually a placeholder for a replacement pitch.
Ask whether flashing is being replaced or resealed. Reseal is a stopgap; replace is a repair.
Common repairs on tile roofs
Cracked or slipped tiles let water onto the underlayment, which is fine for a while and then not. I lift the surrounding tiles, replace the cracked ones with matched pieces, and patch or replace the felt underneath if it has been wet. Ridge and hip caps that have lost their mortar get reset on foam or a mechanical ridge system.
Where the felt has gone brittle across a whole slope I stop and tell you, because that is the point where a repair becomes a re-lay.
Common repairs on shingle roofs
Wind-lifted and creased tabs get replaced, not glued down. Missing shingles get matched as closely as the sun-faded originals allow. Nail pops are pulled, the hole sealed, and the nail relocated. Exposed nails at ridge caps get sealed. Valleys with rusted metal or shingles cut too close to the centerline get rebuilt.
Granule loss across the whole roof is not repairable; that is an age problem and I say so.
Flashings and penetrations
Rubber pipe boots split in this sun within a decade and are the single most common leak I fix. Chimney counterflashing that was caulked to the brick instead of cut into the mortar joint fails as soon as the caulk shrinks. Skylight curbs without step flashing leak at the corners.
I replace the metal and do it the way it should have been done first time; sealant is the last step, not the whole job.
When I will not repair
Soft decking under the leak, underlayment that crumbles when touched, more than one layer of shingle already on the roof, or a leak that has already been chased around by other repairs. In those cases a repair takes your money and the leak comes back somewhere else next winter.
You will get a straight answer and both scopes in writing so you can decide.