To build a large outdoor birdhouse, make a duplex birdhouse with two entrances, gluing and nailing two separate birdhouses together into one unit. Alternatively, buy a large calabash gourd, drill an entrance hole, remove the seeds and membrane, preserve the gourd, paint it white, and hang it on a pole.
To make a duplex birdhouse, cut two 6-inch by 17-inch fence boards and two 6-inch by 12-inch fence boards. With a miter saw, cut 25-degree angle peaks in all four boards. In one large board and one small board, drill a 1 1/2-inch hole about 4 inches from the top of the peaks. Router the holes and front edges of the house fronts.
Cut two sides for each house that measure from the bottom to the roofline. Glue and nail the houses together, with the back of the small house against the side of the large house. Cut two 8-inch by 11-inch fence boards and two 8-inch by 10 1/2-inch fence boards to make the roofs. Cut the tops at 45-degree angles, and then glue and nail them together at the peaks. Add 1/8-inch dowels under the holes for a perch.
Another option is to use a large, preserved calabash gourd as a birdhouse. Soak the gourd in hot, soapy water for 20 to 30 minutes, and then clean the gourd with a scrub brush. Dry the gourd, and then drill a 2 1/8-inch hole in the side for an entrance, and small holes in the bottom for drainage. Remove the seeds and membrane, soak the gourd in copper sulfate for 15 minutes to preserve it, and let it dry for several days. To finish the project, paint the gourd with white house paint and hang from a wire on a pole.