To build ports from a committer account on freefall and related machines.
You can add this to your .profile on freefall.

 * Only your user home directory needs to be writeable.
 * You can build most ports and their dependencies.

 * The home can be shared between different archs.
 * Successful build packages are cached.
 * dependency to the installed "pkg" is lifted.

The PREFIX path I suggest is "/home/<user>/local-<arch>"

Put the following lines in your .profile

# PREFIX will be /home/<user>/local-<arch>
export UNAMEM=`uname -m`
export LOCALBASE=${HOME}/local-${UNAMEM}
export X11BASE=${HOME}/local-${UNAMEM}
export PKG_DBDIR=${HOME}/local-${UNAMEM}/var.db.pk
export PACKAGES=${HOME}/local-${UNAMEM}/packages
export __MAKE_CONF=${HOME}/local-${UNAMEM}/etc/make.conf
export PORT_DBDIR=${HOME}/local-${UNAMEM}/options

# Extend path so we can run dependend programs
export PATH=${HOME}/batch:${HOME}/local-${UNAMEM}/bin:${HOME}/local-${UNAMEM}/sbin:${PATH}
export LD_LIBRARY_PATH=${HOME}/local-${UNAMEM}/lib
export LD_RUN_PATH=${HOME}/local-${UNAMEM}/lib

# Tell Makefile who owns it all
export INSTALL_AS_USER=yes
export WHOAMI=`whoami`
export BINOWN=${WHOAMI}
export BINGRP=${WHOAMI}
export MANOWN=${WHOAMI}
export MANGRP=${WHOAMI}

# ranlib on readonly libs don't work
export SHAREMODE=644

# ldconfig must write, so we change the options
export LDCONFIG="/sbin/ldconfig -i -f ${HOME}/local-${UNAMEM}/etc/ldconfig.hints"

# The place for cached distfiles shared, with all archs
export DISTDIR=${HOME}/distfiles

# Decide where temp build stuff
export WRKDIRPREFIX=${HOME}/work

# Finally we may use our own ports tree
export PORTSDIR=${HOME}/ports

# We like to cache and save the packages
export USE_PACKAGE_DEPENDS="yes"
export DEPENDS_SHOW_FLAVOR="yes"
export DEPENDS_TARGET="package install"

# We use the installed pkg, but do not depend on it
export PKG_DEPENDS=
export PKG_PREFIX=/usr/local
export PKG_BIN=/usr/local/sbin/pkg-static