What about multiple zones?
$BuildZones::PointA[1] = "6, 6, 6"
$BuildZones::PointB[1] = "9, 9, 9"
$BuildZones::PointA[2] = "12, 12, 12"
$BuildZones::PointB[2] = "9, 9, 9"
why not just take the Triggers from cityRPG, change the dimmensions and change the functions.
but i'm far too lazy to actually do any thinking :(