I am adding a porch to an existing house with changing from aluminum to vinyl siding. My question is: Eventhough the supplier sold me flashing go go under the siding it is flat on both sides as you would expect a flashing to be. Shouldn't there be a flashing or cap that fits the contour of the metal roof that goes up behind the siding to create a water tight seal at the roof and siding intersection. I appears to me that if I use the flat flashing under the siding and on top of the metal roof the raised contour fo the roof will allow water to blow back under it and leak down the wall. The porch roof is 4-12 pitch and the flashing about 6 inches wide so it would require a pretty hard blowing rain, but I dont want to take the chance. It is confusing to explan in writing bur relatively simple when looking at it to see the problem. Any help will be appreciated.

A Small Part Of My Roof.. With A Slight Pitch...is Leaking.. Is There A Product I Can Simply Roll On Or Brush On To My Shingles To Stop The Leak.....do I Need To Replace The Shingles