Neighbor's construction interferes with my property so roof leaks

[Adrian Meng]

Currently my flat roof itself doesn’t look old yet. No patch jobs anywhere so My former inspector concluded it might last another 4~5 years more but that was 10 months ago, when I purchased this property.  But the flat roofs are also well known for its headache, water leaking just a matter of when.  The extra walls added exacerbate the water leak risk due to water trapped into a narrow area.  The original flat roof was built for fully open and didn’t consider a completely new scenario like this.  The exterior wall the neighbor newly added has much better chance because it meets the newest building code.  Those material, products, and assemblies utilized on my existing exterior wall 30 years ago are very different. His contractor suggested might want to see about improving the condition of that portion of my wall if I am interested, since the contractor has to return and finish the new wall as part of his ongoing renovation in the coming weeks.  He said that doing any work will be completely at my discretion. They can also leave it exactly it was, in its current state.  I just emailed the neighbor and suggested also focus on the area when the wall meets the roof, weakest link. Things remain preliminary until a description available from his contractor for what’s to be done accordingly.  currently our family lives in the property purchased.  It is our second home for investment but has not be rented out yet.  I would like to receive your advise.  All input are welcome.  Thank you in advance,