Decks, Patios, Porches and Docks - raised concrete porch

HI,
I'm building a new house... with 36'x9' front porch, I have a footer poured and blocks raising the porch about 3 feet.
I like to be able to pour concrete slab on the raised porch, I have seen it done on a new home, where they used Congregated Galvanized sheets as a base, and poured the concrete over it.
since I have a large porch, I'm worried that the weight of the wet concrete will cause the metal panels to cave in, do I need to support it?, if so how?
what is the metal thinkness needed for a job like this?
is there anything else I need to consider before attempting the pour?

thank you all.

I did this exact thing for my mother in law last year. I filled mine with sand and skipped the steel. I attached a 2x2 to the top of the foundation, then attached a 2x6 to that (as a form for the edge of the cap) and staked the bejesus out of it. Before I poured, I was sure to put an expansion joint along the house so that cement wasn't directly in contact with the sheathing. I also put 1/2" rebar in the cap. After the cement had cured a couple days, I cut the cement into perfect squares so that it wouldn't fracture in a bad spot. I also flashed the back side (over the expansion joint) so that it wouldn't trap water and rot.

For the handrail, I ended up having some 4x4 post bases welded up... basically just an 8x8 piece of steel with a 6" section of 4" square tube welded to it. Dropped some cedar 4x4's in (rounded the edges) andmade the handrail and ballusters out of cedar as usual. Primed and painted it all with a high gloss white paint. It worked great and looks like a million bucks! Which reminds me, I still need to take some pictures of that one!