Many wooden house plans do not allow the compartment to be opened and inspected during nest checks. This is very important. Some wooden houses are so heavy that it is almost impossible to have a system to raise and lower it during nest checks. These are a couple of the drawbacks of wooden houses. A properly designed wooden house can be a very good for the martins.
Wood is a better insulator than metal.
This can help keep the heat down in the hot states. The picture below shows a wooden house with a very good design. It uses a winch to raise and lower it. Notice the compartments are arranged so that each male has his own porch. This helps eliminate the male from dominating several cavities.