Technically, there should not be a reason that you could not use wood. However, the problems will be the type of wood (make sure it is not treated with arsenic or other toxic chemical) and finally, the water seal. Birds are extremely hypersensitive to toxins, chemicals, etc. If you use a water seal, you need to check out the toxicity level to fish and birds and its reaction to long periods in water. These toxins/chemicals can also leech into the food supply so be extremely careful. The Regal Swan