I always found some scandinavian death metal played through a powerful hi-fi (rather than those crappy little portable radios) are the best way to piss off chavs. Also if your neighbours (or friends neighbours in this case) are doing some work on the roof, then a well aimed firecracker going by the name of "la bomb" is also a goodie.
If you had chavs in America, then that would solve your problem. Just send them in and they'll destroy anything that is built and probably damage some equipment as well.
Given the size of the place being developed, I reckon a bomb of some sort would solve the problem quite nicely. I'm sure someone who browses this forum knows enough about bombs to recommend an appropriate one.