So build one that can hold two ponies or a large keg, say if you are having a party. Keep in mind a properly cared for keg can last up to and longer than 8 months.
This is a great place to start for ideas. It is a home brew site so some of the fridges are too small or what not, but there are a lot of good images on the pieces and parts that you would need and how to do it.
http://www.homebrewtalk.com/f35/show...gerator-29053/