TO: wtnhunt & readers, We use flashing or valley flashing as some call, for our roofs. Cheapness and durability is what you'll get doing it this way. In the case of a 6x6, you would need a roll of 30" flashing. Cut three pieces 6'-6" long. Fold edges down for extra protection leaving the six feet. Overlap the three pieces on roof. Use sheet metal screws of your liking. Can use OSB under sheet metal or plywood, whichever suits your wallet. Have done this for many, many years. Have never had problems.
Thanks for your interest!!!
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