[CentOS] tutorial or guide to write RPM Spec file

See this page: http://fedoraproject.org/wiki/How_to_create_an_RPM_package

There are a few pointers you should get used to and after a few you'll be fine.

Don't build as root, do something like this:

yum install rpm-build redhat-rpm-config rpmdevtools
useradd rpmbuilder
su - rpmbuilder
echo "timestamping = on" >.wgetrc
rpmdev-setuptree

The vim-common package also provides a template spec, but I would suggest
downloading some srpm's and extracting them and looking at the specs they
have.

wget 'http://vault.centos.org/6.3/os/Source/SPackages/postfix-2.6.6-2.2.el6_1.src.rpm'
rpm2cpio postfix-2.6.6-2.2.el6_1.src.rpm |cpio -dim
vi postfix.spec

Look at a few, google the cmds you don't understand...
jlc