Used on my 11^W12-CURRENT laptop to rebuild FreeBSD from source.

00_clean_src.sh

#!/bin/sh

UPDATE_SRC=false
if [ ! -z "$1" ] && [ "$1" = "-u" ]; 
then
    UPDATE_SRC=true
    if which svn; then
        SVN=`which svn`
    elif which svnlite; then
        SVN=`which svnlite`
    else
        echo ' ! No SVN-client found.'
        SVN=/nonexistant
        UPDATE_SRC=false
    fi
fi

if [ -d /usr/obj/usr ];
then
    chflags -R noschg /usr/obj/usr && \
    rm -rf /usr/obj/usr || \
    exit 1
fi
cd /usr/src && \
    make cleandir && \
    make cleandir

if $UPDATE_SRC && [ -x "$SVN" ]; then
    $SVN up
fi

01_world_kernel_installkernel.sh

#!/bin/sh -e

if [ -f /usr/src/src.conf ];
then
    SRCCONF_PARM="SRCCONF=/usr/src/src.conf"
fi

if [ -f /usr/src/sys/amd64/conf/IPSEC_VIMAGE ];
then
    KERNCONF_PARM="KERNCONF=IPSEC_VIMAGE"
fi

KEEP=false
NO_KERNEL=false
CPUS=`sysctl -n hw.ncpu`
JOBS=$CPUS
while [ "x$1" != "x" ];
do
    case "$1" in
            # Prevents make clean
        -K) KEEP=true
            echo "Does not work as advertised!"
            exit 2
            ;;
            # set number of parallel
            # jobs to run
        -j) if [ "$2" != "${2#/}" ];
            then
                JOBS=$(( $CPUS / ${2#/} ))
            else
                JOBS=$2
            fi
            if [ $JOBS -le 1 ];
            then
                echo " ! Can't run less than one job." \
                    > /dev/stderr
                JOBS=1
            fi
            shift
            ;;
        -N) NO_KERNEL=true
            ;;
         *) echo " ! Unknown parameter '$1'." \
                > /dev/stderr
            exit 1
            ;;
    esac
    shift
done

cd /usr/src

if ! $KEEP;
then
    test -d /usr/obj/usr && \
        chflags -R noschg /usr/obj/usr
    rm -rf /usr/obj/usr
    make cleandir
    make cleandir
else
    echo " * Not cleaning /usr/src before running make"
    sleep 2
fi

/usr/bin/time -o make_buildworld.time \
    nice make -j $JOBS $SRCCONF_PARM buildworld

/usr/bin/time -o make_buildkernel.time \
    nice make -j $JOBS \
    $SRCCONF_PARM $KERNCONF_PARM buildkernel

if $NO_KERNEL;
then
    echo " * Not installing the built kernel."
else
    make $SRCCONF_PARM $KERNCONF_PARM installkernel
fi

02_install_world.sh

#!/bin/sh -e
# based on 
# http://www.bsdnow.tv/tutorials/stable-current

UPDATE_PKGS=false
if [ "x$1" = "x-p" ]; 
then
    UPDATE_PKGS=true
fi

if [ -f /usr/src/src.conf ];
then
    SRCCONF_PARM="SRCCONF=/usr/src/src.conf"
fi

cd /usr/src
## If anything needs to be merged, added or removed.
mergemaster -p
make $SRCCONF_PARM installworld
# You will merge the new config files with your old ones.
mergemaster -iUF
yes | make delete-old
if $UPDATE_PKGS; 
then
    echo "  * Updating packages before removing old libs."
    pkg upgrade
fi
yes | make delete-old-libs
chflags -R noschg /usr/obj/*
rm -rf /usr/obj/*