In article ,
VM wrote:

Looking for something to use as a simple unattached 'floor' for on a
fire escape. Needs to be rain-proof of course. A big sheet of 1/8"
aluminum would probably do it, but I have a feeling that there are
cheaper ways. Anyone know of anything?

How about some grating? McMaster sells steel and fiberglass stuff, but
they may not be the least expensive place to buy it.