Struggling with how to complete deck off 2nd floor bedroom. There are sliding glass doors which lead to small freestanding perch with railings off of bedroom (large enough only for 2 people to stand). It had been started and has wood base with all weather black paper on it but it is not completed as we do not know what to do with it. the intent was to put mahogany decking to match the deck below however water sits on the black all weather paper and does not run off. We are concerned that water can get under the sliding glass doors and may eventually rot out the freestanding small deck (it is freestanding and sits above the outside deck off of the house). What can we do to fix this and to complete the freestanding perch? Should we put wood on top of the black paper or do we need to fix the perch itself in some way first?