[Porchdog]

I may be a bit stuck on our snow loads up here.

I'm pretty skeptical of a rolled roof with no pitch. Also, the rolled roof needs to be nailed down - which could trash the deck for any flooring you eventually want to put on it. The big issue with roofing is uplift - that's why built up roofing frequently has stone ballast on it.

I suppose the if your first floor will overhang your foundation you could pitch it in the direction of the joists to act as a temporary roof. I don't like overhanging decks as they are difficult to provide proper sealing/ weather proofing. They are also prone to mold issues.

For your idea it may be the only way to go. After you take the temporary roofing off and level the deck you will probably need a subfloor to level/smooth out the deck.