variant 1)

switch(..., blah, num_houses >= 10) {
 1: return 0;
 return 1;
}

...
graphics {
 ...
 construction_check: blah;
}

==========
variant 2)

graphics {
 ...
 construction_check: (num_houses >= 10)?0:1;
}

==========
variant 3)

graphics {
 ...
 construction_check: num_houses < 10;
}