Hi I may be able to go to small claims, I think he has a leak on roof and chimney stack

Hi I may be able to take him to small claims

I have spent thousands on damp proofing over many years, I let my premise in 2013 and in 2014 had the whole ground floor damp proofed, replastered and decorated, I also had the roof sorted. I have had to request my builder to treat my walls for patches which are caused from one of my neighbours, I have asked him if he plans to tackle it and he says no, affordability, my property is being badly affected as a result, what can I do?