Fire Proofing

[stinkyattic]

You should build your grow room as sturdy as you can for safety and permanence.

I am going to be doing all the wiring myself and this being the first time ever doing electrical work adds concern.

I wouldn't recommend that. Don't you know someone with electrical experience? You are going to want at least 1 dedicated 20A breaker with a home run all the way to your breaker box, just for the grow room.
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The plans are: The floor will be coated with a layer of duct tape, which is on top cardboard with wood on the spots I where I will be walking.

Well, that's a fire hazard right there. Cardboard is very flammable. And when it gets wet, it rots. And it WILL get wet no matter how much duct tape you put over it.

For the floor you really need at least 3/8 inch plywood. Half-inch is better.

Duct tape is seriously expensive, not a good floor material, and wears through very fast.

Paint your floor with an oil-based white primer. That will keep mold from growing. I recommend KILZ brand.

The walls will be Mylar

That's appropriate!

and the ballast made from an old computer case and silver tape (donâ??t know the name). I wanted to wrap the clip on lamps in silver tape (fire hazard)?

What's with the silver tape? I believe it is conductive too. Just spray paint everything white. Including the lamps. If you can find heatproof white paint that's even better but not necessary.

The floor where the plants go on be made of spray painted white dense foam which I may want to cover in silver tape. The lamps will have 20 watt CFL's and the ballast will have a 400w HPS light in it.

Don't bother with the foam. If you do the floor right, you can just put them on the floor. I like to put mine in kitty-littertrays ($2 each from Family Dollar) to avoid spills and mess, and to make everything easier to clean. You can just pick up the whole thing and slide it around.

Standing temperature of the room is about 70 degrees, how much will this go up? Estimates of Mylar room being 8x8 with slanted ceiling 5.5 feet at its tallest, the grow spot being 4x4.

It will go up when the HPS is running and you are going to need exhaust fans.

I would love input on ... fire proofing trial and error

There's no trial and error in fireproofing. Take it seriously. Your house burns because you did the wiring yourself to grow pot, your insurance policy goes out the window.

My final advice is, the plan you had will end up being MORE expensive even just for materials and super pain in the ass to install. Just do it solid the first time. Get an electrician to install a bunch of outlets for you up there and tell him or her that it is going to be for a future cooling unit that you are going to install yourself or something... or a photographic darkroom... or whatever. be creative.