Construction Bird houses, or nest boxes, can be fancy or simple. This article discusses simple designs. Slabwood leftovers from a lumber mill will do nicely. One can even consider a section of hollow log found in the firewood pile. The diagram in this article offers one design.
Fancier offerings exist for waterfowl, bluebirds, owls and purple martins.
Interior sizes vary depending on the bird species as shown in the chart. When using lumber of different thicknesses, keep in mind that inside dimensions are the most important to birds. Do not attach a perch outside the nest hole. A perch helps nest raiders attack occupants. Drill a few holes in the floor of the house to allow water to drain.