[CentOS] Creating my own YUM repository

I have already 6 Centos machines here and it is getting strange having to pull down updates to each system.

Seems like I should set up one system to pull updates and then all other systems to point to it.

How?

Plus then I would want to add to this repository.

Say that a number of my systems use tomcat which is only available via rpm. I would like to be able to add it to my repository, and if even manually, to keep it current. This way, when I build a new system, after the build I would do a yum update (from my server), then a yum install of all of the extras that particular system needs.