Following the lifting up and installation of the roof trusses, I opened the main roof and built the diminishing trusses from the old roof structure to the new trusses and started on the construction of the valley between the two roofs using a timber valley covered with a GRP trough.
The photo below shows the timber backing with the breather membrane covering prior to the GRP valley being installed.
I decided to put a temporary sheet over the whole roof to stop my joists and trusses getting soaked and warping. This made life easier and more difficult in equal measure. I used the 2000 gauge DPM that I had left over from the concrete floor. I stapled it and then realised the wind was going to lift that straight off so ended up battening it down.