Regular use one has to assume chair legs and inappropriate footware will
be an issue.

For irregular access, add aluminium and copper and maybe EDPM rubber.

Personally, I'd go for zinc, or copper if it's out of the way of pikey
prying eyes.

Tim, Yes chair legs etc will definitely bbe an issue. The roof will get the same wear and tesr as a regular back patio. When you say copper/zinc, is that just the covering? What about the underlying support?
J