Are there tutorials available in official CentOS documentation for writing 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....' 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