My wife and I are starting to build a custom home and instead of a regular deck on the back of the house, we want to tile the floor, and have masons stucco and brick the posts and sides.

Two contractors have had two different construction methods, and I'm looking for some professional opinions on them. Both would frame the "deck" with PT lumber, 2x12 joists, and then they diverge.

Contractor 1: Use PT plywood, screwed and glued to joists, cover with DuRock, Tile on top, seal tile.

Contractor 2: Use corrugated (sp) steel on joists, pour and smooth concrete on steel, Tile on top, seal tile.

We're in northern SC, southern NC, where we get very few freezing temps, if that matters in your opinions.

First question: Could we use I Joists instead of 2x12 PT? I'm concerned about warping and shrinkage of PT Lumber.

Second: Poured Concrete base or plywood & DuRock?

Third: If we use plywood and DuRock, should we use two layers of plywood for strength?

Thanks for your opinions.
Brian