The main portion of my 1950's house has a large shed-style roof (the top edge is the end of the roof...it doesn't slant back down the other side). I've had a very slowly building leak at the lower corners of the chimney that is evident inside (the ceiling is cathedral style so the drywall is right up against the rafters).
I had a guy out today to look at it and he says the drip edge on the top edge was installed incorrectly. Whereas you want the drip edge under the shingles at the bottom, he says on my roof they were also installed under the shingles at the top. That, combined with the shingles not quite covering the drip edge on that top roof edge is allowing water to flow under the shingles. Then the chimney pokes through the felt and that's where the water is coming in. He says everything looks tight and solid around the chimney itself, which is what led him to keep looking.
He proposes to install drip edge on top of those shingles and seal it up, thereby keeping the water from coming in.
Does this make sense? I did some searching around, but couldn't find anything about the proper way to deal with the top edge of a shed roof.