I just put a piece of galvanized sheet metal on the roof about 3
shingles op from the edge of the roof. I bent a 2" wide 90 degree in a
6" wide piece of metal 4 feet long. slid it under the shingles, no
nails. I used some clear silicone to hold it in place. When we
replaced the roof years later, we had gutters installed.

Stretch