i used this plan
http://2hot2cool.com/4/afishianado/afishian.htm

and this is the same thing except the coils are on the outside.
http://www.aquariumpros.ca/forums/sh...ad.php?t=18394

project costed me about $40-$50 and a few hours time. wasn't too difficult, most difficult part was to get the coil wound up in the inside.