That sucks. The only problem with leaks is that they don't get any better.
Be careful with that and stay on the builder and your neighbor to make it right.
you don't want to wake up one day to chunks of your ceiling in your sink. Not to mention the water pooling up there creating a petri dish for whatever's next.
we have the luxury of local building inspectors around here who would also take care of that sort of thing, but I'm not sure if you have that option.