Paul wrote:

Or, is it just too hard and too heavy? I was thinking of tongue and groove
floorboards on a wooden or metal frame.

I think it would be very heavy, which would make it [a]
difficult to build and [b] difficult to install once built.

There's a big diffenence in weight between 1mm steel sheet and
12mm timber.

If you do do it, you'll definitely need a steel frame - a timber
frame will just flex too much at that size (unless you use
massive timbers, which will make it even heavier).

--
Grunff