BirdsAndBlooms.com offers a free plan for building a simple birdhouse. The easy plan requires one 5-foot length of 1-inch by 6-inch pine board, galvanized deck screws, 2-inch galvanized finishing nails, a hand saw, and a power drill with a spade bit.
Plans for building birdhouses for wrens, chickadees, nuthatches, woodpeckers and tree swallows are found at 50Birds.com. The site also offers do-it-yourself plans for constructing birdhouses for prothonotary warblers, bluebirds and yellow-bellied sapsuckers.
Birdwatching-Bliss.com recommends drilling drainage holes in the bottom of a birdhouse. It also suggests omitting a perch from homemade birdhouses to prevent squirrels and predators from bothering nesting birds.