Greetings, regarding using good quality plywood for tops, we have been using recycled plastic for tops for some years now without noticing any negative attributes. It comes in 4 x 8 sheets in various thicknesses, cuts like ply, and nails or screws like ply. Doesn't need any painting and my well be indestructible. I use migratory lids and during the first few years we checked its compatibility with the bees and noticed no obvious negative effects, they wax and propolis it just as wood. Peter -- Visit www.honeybeeworld.com/bee-l for rules, FAQ and other info ---