This design is so simple that basically you can just look at the drawing at the left, and the cutting patterns at the right, and figure out most of what you need to do. The entrance hole is 1½-inch across. It took me about an hour to construct the whole thing.
In the drawing at the left, notice how you can design the box so that the door hinges outward. This enables you to clean out old nests at the end of each season, so that over the years parasites don't build up inside the box. For my own box I nailed the front on, but on the roof I used small nails that held the roof securely, but not so securely that when box-cleaning time came I couldn't just hit the roof from below, with a hammer, and knock it off. Then later I'll set the roof back in place and maybe add a nail or two.
I didn't have a drill attachment enabling me to cut the 1½-inch-wide entrance hole. However I did have a drill that cut small holes. Using that and a wood chisel, I gnawed at the hole until it was good enough.
The floor should have places for water to drain out. You may want to cut the floor's corners before nailing it in, or maybe drill holes in it. Just remember the drainage problem, and don't make a hole larger than about ¼-inch, else snakes might squeeze through.
The nest should have ventilation, too. When I nailed on the back, I made sure that between the back and the roof a space of about ¼-inch width was left. Again, you don't want larger holes or snakes will have easy entrance.
Mount nest boxes 4 to 6 feet above the ground on a metal or wooden post. Place your box in an open grassy area with widely scattered trees and shrubs. To keep other birds such as wrens and sparrows from taking over the nest box, it's best to put the nest as far from buildings as possible.
It's best to equip the post with some kind of "predator guard" to keep snakes and rodents from climbing the pole.
All kinds of information and activities relating to bluebirds is available at the North American Bluebird Society Web site. Another place to find detailed information about Eastern Bluebirds themselves is the USGS Eastern Bluebird General Information Page.