Hi, Scott,
From the North American Bluebird Society:
http://www.nabluebirdsociety.org/eastwestbox.htm
I've had good luck with this basic plan. You can make them out of cedar, pine or whatever you have on-hand. Rough-sawn works best. These plans allow for ventilation, drainage, and easy access to monitor the nest as well as clean the box out.
Bluebirds can be fairly picky but basically if you site them right, the birds will use them. I've had bluebirds, chickadees, titmice and wrens use mine over the years. Anything smaller than a bluebird will use a bluebird house.
If you want to go bigger, you can probably find plans around for Screech Owls, Flickers, red-bellied woodpeckers and wood ducks.
I go more for practicality when it comes to nest boxes intended for actual use by our feathered friends. The fancy houses can be designed for things like cleaning, ventilation, etc.
PM me if you need any other links to different nestboxes.
:kermit: Steve