Seriously, what the h-e-double hockey sticks are people talking about up in here? It's like we're trying to go all west coast customs on a friggin beer pong table.
Simple. Easy. No frills.
Buy a 4 foot by 8 foot piece of Pressure Treated Plywood. Pressure treated plywood is designed for outdoor exposure, used in decks, swingsets, tree houses, and anything else that can stand up to rain, termites, and is resistant to warping, rotting, and splitting. $27 at any Home Depot store.
http://homedepot.bighammersoftware.c...a-7ffcb932860a
Buy an oil-based primer, coat with that first, and then paint it however you want. Or just go straight with stain and Thompson's Water Seal.
This will give you a beer pong table that works and holds up to the water. I can't tell you much about pimping it out, but this will be simple and cheap.