# to get sources
cd /usr
#export CVS_RSH="ssh" #redundant, by default
export CVSROOT="anoncvs@obsd.cec.mtu.edu:/cvs"
cvs checkout -r OPENBSD_4_5 -P src
# to update sources
cd /usr
cvs -q up -r OPENBSD_4_5 -Pd

# doing work:
$ cd /usr/src/sys/arch/i386/conf
$ /usr/sbin/config GENERIC
$ cd /usr/src/sys/arch/i386/compile/GENERIC
$ make clean && make depend && make
$ su
# make install
# reboot

# rm -rf /usr/obj/*
# cd /usr/src
# make obj
# cd /usr/src/etc
# export DESTDIR=/
# make distrib-dirs
# cd /usr/src
# make build
# reboot