How do you know when to replace your roof?

The answer to that question is multifaceted. Leaks in the roof, age of the roof, and cost is a big factor.
Leaks in the eaves can damage plywood, fascia, soffit, and trusses.

no leaks in the house, plenty at the edges

this type of leak is caused by improper application (workmanship)

 Leaks in the home can do similar wood damage and also create serious health issues with possible mold growth. Repairs to older roofs can be difficult and that would be part of the equation

Do you think they waited too long?

this looks right into the kitchen

about three days of wood work

another issue that we can look at in the next blog will be: Should I wait for a storm to blow off my roof so the insurance company will pay for it?  DUH