Yesterday (25th) was spent resetting and rechecking the dormer beam positions and planning the valley rafters and jacks. We soon realise that the earlier plan was incorrect and the layout needs to be worked out from the apex of the dormer valleys. We need to get the valley rafters at 45 degs and at the same pitch as the roof. We need to ensure the dormer pitch is the same as the main roof.
Like all advanced engineering projects string and cardboard is the way forward.