using Styrofoam or polystyrene 2in thick and caulk to "GLUE" it together. the dimensions are up to you. mine was quite simple, take a case of beers and that's the length and breadth of your cooler box. take a second case and place it on top and that's your height. this height is the same as a bottle of wine and you can fit at least 12 bottles and a dozen beers or cyders. enough to cater for a small afternoon party around the pool
Step 2: Options
this is where it can get interesting. you could leave it as a Styrofoam floating coolerbox or, as I've done, use it around the entertainment area.
for the floating coolerbox add a lip around the top of the box so that your floating surface is bigger. if you don't do this you'll end up with a sinking box.
Step 3: Drainage
ok so your Styrofoam box is built. what happens to all the melted ice? so you need to add a drainage point. I chose a 1in hole with a 90 degree elbow attached to a pipe slanting away from my entertainment area. I found it better to keep the meted ice in the cooler to keep the contents colder and drained it the next day.
I say the next day because I still had ice in the cooler 24 hours later.