The easiest way to track build failures is to receive the emailed logs and sort them to a folder, so you can maintain a running list of current failures and detect new ones easily. To do this, add an email address to ${branch}/portbuild.conf. You can easily bounce the new ones to maintainers.
After a port appears broken on every build combination multiple times, it is time to mark it BROKEN. Two weeks' notification for the maintainers seems fair.
Note: To avoid build errors with ports that need to be manually fetched, put the distfiles into ~ftp/pub/FreeBSD/distfiles.
This, and other documents, can be downloaded from ftp://ftp.FreeBSD.org/pub/FreeBSD/doc/.
For questions about FreeBSD, read the documentation before contacting <questions@FreeBSD.org>.
For questions about this documentation, e-mail <doc@FreeBSD.org>.