On our 2-storey screened porches we use T&G plank decking and a rough sawn fir plywood ceiling. The ceiling was finished in a semi-transparent stain and looked great. Battens can be used around the edges to further refine the look. Be sure to wire in any ceiling lights and switches you want first. The ceiling can be attached directly to the joists or rafters above. If the floor of the second story is not T&G, debris can fall through onto your ceiling below. It also limits being able to hose off the floor deck.

This response is a bit late, but if you have questions, feel free to post back or start a new thread. We didn’t mean to ignore you, but sometimes it happens.