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[Band_Member]

I don't know if this might help you some.

I built a roof (so to say) under my deck where there is a concrete patio. I wanted for us to be able to sit out there while its raining without the rain coming through the deck and dripping down on us.

I ripped strips the lenghth of the deck joists (in my case 10') out of 2x treated material figuring a 1/4" per foot pitch. Over 10' the strip went from 2 1/2" to nothing. I ripped as many as I needed for every joist above the patio. Then I predrilled the screw holes on the strips. I glued and screwed (s/s screws) the pitch strips on the underside of the joists with the 2 1/2" end away from the house.

This provided the pitch for the water to run away from the house on the top of the 1/2" treated plywood that I predrilled and screwed on next using a lot of caulking especially around the screw holes.

I'm thinking you can do the same then frame your shed walls up to it. You can also put a gutter where the water spills out and lead it away.

If anything accumulates up there (twigs, leafs, etc.) just break out a backpack leafblower and blow it off.

Just a thought. Maybe it'll work for you.