The amount of wood required to build a birdhouse depends entirely on the size of the birdhouse. As a rule of thumb, a birdhouse shouldn't be much smaller than 6 inches cubed, otherwise there will not be adequate space for a bird inside.
The basic shape of a birdhouse is a cube. The woodworker must therefore have enough wood for six sides. The wood does not need to be thick as long as the length and width is at least six inches. A birdhouse with a width, depth and height of six inches can be built from a single wood plank with a width of 6 inches, a depth of 1 inch and a length of 3 feet.