I built the 1st one from scratch with no pattern.......the size depends on the cooler you will use, each cooler is different, also the cooler must have a drain to run plumbing.........I use a Coleman 48qt cooler........youtube has some videos on how to build a "cooler box"......I watched plenty, then attempted to build mine......had some struggles at 1st, how much material to buy, what actual plumbing fittings I needed ect. for the drain, , but I've made 25 of them now and I can make one in 3hrs give or take.