Auto Monitor New Users Or Directories

Hi,

I have a server where new directories are created automatically in /var/www
/htmleach of these contains a site and is attached to a new system user
also created at the same time.

I do not have a way to limit these directories for disk use, so would like
to be able to monitor them for size and alert if they go over lets say 1GB.
Thing is I cannot be creating a new rule in monit for every new user or
directory.

I can't find anything on how I might accomplish this. Has anybody done
anything similar with monit and mind sharing an example?