When patching stops being worth it

Daylight or damp in the attic

The attic tells the truth earlier than the ceiling does. Staining on the underside of the deck predates any stain you will see downstairs by a long way.

The age on the paperwork

If the roof is over twenty years old and made of asphalt, an inspection is worth doing whether or not it is leaking. The failure modes above are much cheaper to catch before the water arrives than after.

Shingles that curl, cup or go brittle

A roof near the end goes hard. Shingles that were pliable enough to seal down in the sun no longer bond, and the first serious wind takes them.

Repeated repairs in different places

When the leaks stop clustering and start appearing anywhere, you are not fixing a fault any more. You are paying for a replacement in instalments, at a worse rate.

Sagging along a line

Straight lines going wavy means something underneath has softened. That is no longer a roofing question with a cheap answer.

Granules in the gutter

Asphalt shingles are protected by a granular surface. When that surface starts washing off in quantity, the mat underneath is exposed to ultraviolet and the clock speeds up sharply. A handful of granules after a new roof is normal shedding. Cupfuls, years later, is not.

In short

None of these on their own settles it. Two together usually do. An inspection costs little and removes the guesswork entirely.