My wife and I are hoping to be moving some time in the future and I am wondering about building my own housing unit.

My question is... If I build this unit out of Oak or Walnut do snakes have any ill effect with a varnished finish on wood? With building it out of wood and the snakes needing such high humidty if the wood is not finished it will rot very quickly. I know alot of people on here love there racks, but I love to work with wood and am looking forward to building my own enclosure if it will be safe for my snakes.