Use a circular saw to take the pallets apart. Cut the wood off the 2-by-4-inch stringers and discard the stringers.
Cut the wood into seven pieces. You will need: two pieces for the front and back walls measuring 5 1/2-by-4 1/2 inches with an 90 degree angled gable, two pieces for the side walls measuring 5 1/2-by-4 1/2 inch, one base piece measuring 41/2-by-6 inches and two roof pieces measuring 6-by-5 inches. Drill a 2-inch circular hole in the front wall.
Sand the edges of the wood pieces to remove sharp points.
Hold the four wall pieces up and put them together so that the outer surface of the side walls are flush with the edge of the front and back walls. Hammer nails through the front and back walls, into the side walls.
Place the walls on the base so that the outer surface of the back wall is flush with the edge of the back wall. You will have some excess space jutting out beyond the front wall as a porch. Hammer nails through the bottom piece into the bottom of the walls.
Make 45 degree angle cuts in one edge of each roof pieces so they fit together nicely to form a 90-degree angle roof. Place this angled roof on top of the walls of the birdhouse. Hammer nails through the roof and into the top of the walls to keep them in place.