From the roof of St James church I could clearly see the 'state' of the roof at the old Barnes building ( a sight for sore eyes).
image.jpg
Your friend would probably have to prove that either the building was left in a state that it shouldn't of been left in resulting in damage to his property or that after the problem arised there was neglect (failure to act) on their behalf through not getting 'urgent' repairs done which caused damage that repairs would of prevented.
I hope your friend get the damage sorted asap.