Deck over screen porch attached to house

Deck and screened poarch would be new construction I am looking for ideas to help eliminate water leakage and have a level deck. The deck joists (2x10) will be 10' plus 2' cantalevered over a beam. The deck will be 24' long. The joists well drop 6" total or 1/2" per foot over the 12'. I would use t&g underlayment covered with a seemless product. Over the seemless product I would like to use ripped 2X sleepers to reduce the slope of the final deck to an inch over 12'. Composit decking would be screwed to the floating sleepers. Will this work? Anybody have any other ideas or any ideas to improve on this solution? thanks tom
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