Two planks glued to form a board 6′ or 150mm was the basis for all of these birdhouses. I used 6 pallet planks in all.
The flat roof house is hinged on the back and the other two have to lift off roofs for maintenance. Round holes are 32mm and Robin slot is 50mm high. The peg on one box is from a garden cane. All joints are glued and screwed. Hole in the back at the top to hang the box on a nail or screw.
Made these three pallet birdhouses in a few hours.