Here's the sight that greeted me as I walked into the shed yesterday:
Internal view of the roof over the engine room.
The wooden battens are treated roofing lats.
To follow the curve of the roof without splitting, the lats each have a few transverse slots cut before being screwed in place
These are fixed into the 25 x 50mm channel before the roof sheets were put on. The screw heads therefore don't show as they are under the roof sheet.
View along the roof .