There are many free bluebird box plans available on the Internet. You can also contact your local Cooperative Extension Service office and ask if they have plans.
Bluebirds prefer a mixture of open grasslands and scattered trees, so they are often called a forest “edge” species. Appropriate bluebird grassland habitat consists of open meadows, pastures, yards, cemeteries, parks, and highway right-of-ways. In summer, in these habitats, they consume grasshoppers, flying insects, beetles, and caterpillars during short foraging frays to the ground from an elevated perch.
In the Bluegrass region of Kentucky, the birds prefer a wooden box and seldom nest in milk cartons or soda bottles. Birds in this region prefer the wooden box to have a slot-type entrance (the Kentucky Bluebird Box). Use the slot entrance box if you have problems with starlings or house sparrows nesting in the box. Mount nest boxes on fence posts, metal posts, trees, utility poles, buildings, or fences 3 to 5 feet above the ground. The preferred mounting site is a metal post.
Many free plans for building bird houses can be found at Building birdhouses. Region-specific plans for bluebird boxes have been published by the North American Bluebird Society and can be downloaded at Bluebird Society.