On Tuesday, May 11, 2021 at 5:20:10 PM UTC+1, Chris Bacon wrote:
On 10/05/2021 11:27, cf-leeds wrote:
It's a flat sloping roof with a single gutter across the back end of the garage - It's a prefab garage. (not a pitch roof).

I thought I'd just look online for some galvanised corrugated metal sheets, around the same dimensions at the old asbestos, but I find there are many products out there, including corrugated bitumen sheets.
I'm doing a similar thing. I think I'm going to use 3" corrugated
galvanised rather than plastic coated, on 11mm Sterling board. I don't
want bitumen or felt, might use EDPM but prefer corrugated.

I've built two sheds over the last 30 years and both were roofed in galvanised corrugated steel. It was the cheapest I could find and has lasted so far with no sign of degradation. Its what farm buildings traditionally used.