After serious thinking Rob Graham wrote :
Some dozen years back my good wife had a mid life crisis and bought a Mk1
Mazda Mx5. I was obliged to quit the garage for this wee monster so that it
could comply with the insurance company's requirements. So additional
storage space had to be found for my wood store and somewhere for my lathes.

There was a vague open lean-too structure already on one side so that was
formalised with a proper floor, walls, etc. The small pitch corrugated pvc
roofing was recycled and patched up. It is is this that now needs replacing,
not critical, but it would be better to do this summer.

But with what? There's no windows in this 'shed' so roof light is the norm.
I thought of conservatory roofing but then realised that I would have to
totally change the roof framing for that for jointing the panels.

Any suggestions ?

The 'shed' is 4 x 2m with nominally 4 x 2" roof timbers at 800mm centres, and
a fairly low pitch angle.

Thanks
Rob

Aside from the lack of a transparent to light area, I would suggest
galv coated steel cladding sheets. Long lasting, available in several
colours and not expensive, but buy the thicker grade if you might need
to stand upon it for some reason in the future.