I can't see why they have moved so I assume they have simply bent a little between the ridge pole and the purlin. The ridge pole appears to be still straight, and the corresponding rafters on the other side of the roof are ok.
Is it better to leave the slates and timbers where they are, and try to reinforce the timbers from the inside, and if so any suggestions on how to do the repair?
Alternatively, should I remove some ridge tiles and slates, and try to add new sections of rafter from the outside?
Or some other method? Any practical hints gratefully received. It's a barn with stone walls, roof span 9.3m (30ft). Three purlins on each side. Rafters 50mm x 50mm. Quite old, but I don't know how old. Cheers, James