I have a flat-roof dormer similar to the one in the picture I included. I am in the process of replacing the roof with dimensional shingles. There is a porch of lesser pitch in front of the dormer as pictured. The dormer currently has no gutter. I know that water from the dormer will have to make contact with the porch shingles in some form or another. Which would be best for the life of the shingles below, with or without a gutter? Thanks.