My wife and I put on a wedding party for some close friends. We had never had a party at our house for more than 60 people. So besides constructing a 60 square foot buffet table in our garden. I also wanted a large cooler for soft drinks and beer. A trip to our local big box store netted me: 1 2'x4' sheet of 1' rigid foam, a 4'x8' sheet of 2" rigid foam and seven 8' 2x4's (mystery "white" wood). If I was building this cooler to be a permanent outdoor fixture I would have used redwood or cedar. I iced 5 cases of beverages with plenty of room to spare. This design is scalable to whatever size cooler you need.

Step 1:

Start by assembling the base and top, they are identical with the exception of the bottom having a brace in the middle. The inside dimension is 24" x 32.5". Basically the frame is just 2x4's screwed together with 3 inch deck screws at right angles.

Step 2: Place the Rigid Foam

My foam pieces: the bottom is 1' foam 24" x 44.5", sides are 2" foam 18" x 44.5", ends are 2" foam 18" x 20". everything should fit tightly together. I had an extra piece of 24" x 48" x 2" foam I used for a loose top.