I built an outdoor sandbox for the kids that's about 4' x 5' but haven't had the time to put a real roof on it yet. To keep the rain (and the poo of roaming cats) out, we have thus far been using a piece of plastic sheeting held down with a bunch of bricks on the edges, but we have to go out and empty a giant puddle of water from the middle of it after each rainstorm so obviously that's a temporary solution.
I would like to build an extremely simple and inexpensive lid/roof for the box that will last at least a few years. Shingles seem like overkill, but all of the ideas online that don't use shingles seem like they're going to fail as soon as they get wet (ie this guy who just painted an OSB sheet).
What would be a good material for roofing? Can I just tar some plywood? Would painting OSB actually work long-term?