Look for this common issue...
This is a really common issue that I see every week when I’m out inspecting roofs.
On some houses the shingles are replaced, but some of the flashings are not.
What you are looking out for is the flashing set in the chimney, called Step Flashing. When they just shingle over it there are two problems.
The first issue is that it’s no longer step flashing and won’t work properly.
The second problem is that the flashing will probably rust out before the roof fails. So make sure you specify when your roof is replaced that all flashings will be replaced!