"Where the rubber meets the road" is a phrase meaning "The time or place where you have to prove yourself." That's where you find out for sure whether you're good enough. That's where you can't rely on talk, but can see how something really performs.
For your roof, the phrase ought to be, "Where the roof meets -- the roof."
The points where one surface of a roof meets other surfaces are places where any skimping or shoddy workmanship is going to show. Check those areas and see whether it's time to call a roofing contractor.
