Ported box plans

Are there any places that will tell how to build a ported sub box? I have been looking for a while now and have found none. Theres got to be somewhere that at least gives a starting point on building a ported box. I just want to see if it would be in my ability to build one for my next project. Thanx.

http://www.diysubwoofers.org/prt/
http://www.the12volt.com/caraudio/boxes.asp

It's almost the same process in building a sealed box but allowing for the port(s).