Any 'honourable' person would assess the situation from every angle.
That would include getting up on the roof and checking those 'capping tiles' close up......removing an odd one if necessary for a peek beneath.
He would then get into the loft space, and look for water ingress (there's always a trace), feel for wet insulation etc and see how far the water had progressed.
He would then check in the room below the problem area for blown plaster and so on.
Its unfortunate that there is no access next door.
Now - no one is blessed with X-ray eyes so a 100% proposal can't be guaranteed, but it sure would be closer than what you've experienced so far.
So far as I see, checkatrade and rated people are a waste of time and I wouldn't even waste my time there.
John
I thought the same about checkatrade etc. there's zero negative feedback and everyone seems to score over an 8 which is completely unrealistic because you can't please every customer. No matter how good you are.
I've asked friends and they can't recommend everyone so I'm left with little option but to pick random names out of the yellow pages.