I made this out of 4 2x4s, about 4 or 5 feet long. Screw them into a square with big ol' drywall screws at the corner. Then tie two ropes across the centers in a cross and put a tarp over the top: the ropes mean your tarp divides into four "buckets". Use zip ties to hold your tarp in place. Tie some long ropes to opposite corners, and suspend from a tree and you're nearly done. The all important final touch is hanging a beer opener on a bungee off the middle. Fill with ice 'n' beer and away you go.