It's that time of year. Cabin fever got you down? Build some of the above linked wood duck houses and take a nice walk in a frozen marsh. Help out some of your good wildlife.
I've used these particular plans. The woodies like them and they use less wood than others I've tried. I build mine from pine as cedar is super expensive locally and give them a good heavy coat of linseed oil, especially at the wood-to wood joints. I've got one up built from pine 10 years ago that has raised a clutch every year and shows no signs of serious rot. Use spiral fluted cedar siding nails, they hold a long time.