The roof is approx 2500mm x 3500mm. Panels come in 2,000mm x 950mm.

To allow overlap roughly how many would I need?

I’d say 10 to be safe?

Depends which way the roof slopes.

Assuming the corrugations run lengthways on the sheets…

If the slope is the short side i.e 2500mm then 10
If the roof slopes on the long side i.e 3500mm then 8

if youre on about that onduline stuff (those measurements sound familiar) i was looking into this a week or so and plumped for ply and felt in the end. what i did find out tho was the 950 needs to be calculated at 850 i think as you need a ‘2 corrugations overlap’.

6 if grooves are length ways on the sheet and and paralel to the shortside.

Assuming the 850 dimension syated above. And a 250 overlap on the wavey end.

I just CADed it up for you.

Another sheet as you might just need a long slither.

Easy 6 if the roof slopes the other way.

Thats if you approximate measurements aren’t too approximate.

The roof slopes slightly lengthenways from the entrance to the rear

corrugated generally needs a minimum drop. 10% I think for onduline.

and it’ll sag at that angle if you don’t fully support it.

There’s a wooden framework in place under the existing old corrugated roofing

Well if there is a roof already there, count how many panels there are and buy that many.

Why not use box profile ,easier to fix with correct self drill fixings,coated so will last a life time.

If you’re on about the brittle shattery shite used for covering conservatories I’d recommend not trying to cut the **** stuff with a saw. 2 years on I’m still finding shards of the stuff in our lawn. Aaarghhhh!