Screened in porch under Deck

I am having trouble picturing what you are saying - the porch is under the deck? The deck is coming off of the second story?

Deck Plans
I want to build a Deck off the second floor. I want to make a screened in porch under the deck. I'm not sure how to build the screened in porch's roof under the deck. I want it waterproof as well as have the ability to make it a four season room in the future.

Any help is appreciated

Well, in concept you'd make it like any flat regular roof, so that it is impermeable, and drains correctly. Top and bottom finish would be for looks (if there is room, there could be regular deck on top, that water goes through to the impermeable layer.

You should have your design reviewed by an architect or structural engineer, or at least the building department (it needs a permit anyway) because you want this structure to hold a load of humans and the support system, including provisions against sheer forces, is very important. That deck needs guard rails to code as well. Really, calling a local licensed architect is a good idea. They could design it properly and you could build it. You could also call a licensed general contractor to do both.