Greenhouses, Sheds and Sun Rooms - Sunroom subfloor

We are turning our screened porch into a sunroom. Our problem is the floor which is a slab of concrete is level with the grass outside. We fear water can flow into the sunroom. We want to raise the floor which is a slab of concrete,with a subfloor (like a deck) add plywood and 'durarock' and finish with tile. Can this be done? Do you foresee any problems? Do you recommend insulating this subfloor? Can we put this subfloor directly over the slab, can the wood touch the concrete-any moisture problems? We are thinking of doing everything first, putting in the windows, doors and everything else and the last thing would be to raise the floor? Any suggestions?

I would recommend leaving the slab just as it is and simply putting a french drain around it so that the water couldn't get inside the room. A trench 6" to 8" wide, a foot deep,with perforated ADS in it, and filled with 3/4" rock. Connect that ADS to solid ADS for a discharge line and run it away from the room and house to a gutter or storm drain.

Tile directly over the concrete.