On Tuesday, 4 August 2020 12:43:27 UTC+1, RJH wrote:
On 4 Aug 2020 at 11:10:13 BST, "TimW" wrote:

This is an ordinary timber garden shed 8' x 10' (2.4m x 3m), the roof is
felt on treated sw boards on 3x2 purlins, a central ridge and a shallow
pitch of maybe 15deg. Very standard cheap wooden shed. Over 20 yrs I
have refelted and half re felted and it's leaking again, and the soffit
boards are totally rotted. The rest of the shed is of no particular
quality, and a a bit wobbly.

I was thinking of covering the roof with something better, hoping to
extend its life and usefulness - what would be good? Onduline?
galvanised steel? plywood and a rubber type sheet? some kind of new
material?

FWIW, I've used a sheet of this to cover tools/bikes in the garden (supposed
to be part of a project that never happened), and it's still in one piece and
waterproof after 6 or 7 years:

https://www.roofingmegastore.co.uk/c...eet-green.html

Yes, I have used this stuff. Ten years and still good.