Cover your work surface with newspapers so that you don't accidentally get glue or paint on it.
Drill a 1-1/2-inch-diameter hole in one of the triangles. This will be your bird's door.
Glue the 6-1/2-inch side of the base of each triangle piece to one of the 6-1/2-inch sides of the front and the back pieces. Hold the pieces together for a moment to allow the glue to set. Allow the glue to dry for as long as directed on the package.
Place the floor of your birdhouse on the newspaper in front of you. Place the front and back of the birdhouse at the front and back of the floor. The floor and the face of both the front and back of the birdhouse should all be resting upon the newspaper. Glue the front and back to the floor. Hold the pieces together for a minute to let the glue set.
Apply glue along one 6-1/2-inch base and both 5-inch sides of the sides of the birdhouse. Slip the sides between the front and back pieces and rest them upon the floor. Allow all the glue to dry completely.
Apply glue to the top of the angled edges of the front and back of the birdhouse. Place the roof pieces atop the house and hold them in place for at least a minute to allow the glue to set. Allow all of the glue to dry for at least 24 hours.
Paint your birdhouse to make it fancy. You can decorate it like a diner or you can pick out vivid colors and patterns. If you aren't worried about whether you actually attract birds, you can also paint your birdhouse with designs. Only use latex paint, though, because oil paints are toxic to birds. You also must not paint the inside of the house or else birds will never go in. Allow all paint to dry as directed on the package.
Paint the outside of the birdhouse with polyurethane finish to weatherproof it. Allow the finish to dry completely before you put the birdhouse outside.