You can build a simple bat house in a few hours. For materials, you need a 2 foot by 4 foot section of exterior grade plywood, a 6 foot length of 1-by-2-inch board, 1/2-inch deer netting, caulking, exterior latex paint in a dark color, 3/8-inch staples and 1-inch and 3-1/2-inch deck screws.
Measure and cut the wood
Measure and cut the plywood into two pieces. One piece should be 2 feet wide and 26 inches long, and the other should be 2 feet wide and 22 inches long. Cut the 1-by-2-inch board into three pieces. You will need one 24-inch piece and two 19-inch pieces.
Attach the pieces
Use caulking to attach the longer piece of board to the top edge of the larger piece of plywood. Clamp it in place, and use 1-inch screws every 6 inches to secure it in place. Attach the shorter boards to each side of the plywood piece in the same way. Clean up any excess caulk with a damp rag.
Paint the box
Paint the inside of the box black. You can choose a different color for the exterior, but make sure to use a color that will create a good temperature inside. Dark colors absorb sunlight and make the house warm and comfortable for bats. Paint every exposed surface, and let the pain dry completely.
Attach the deer netting
Use a staple gun to attach the deer netting to the inside of the back section. The netting should lie flat against the back and should be pulled taught. Wrap it around the bottom edge and secure it to the back of the box.
Attach the front
Put caulking along the top of the 1-by-2 inch boards. Making sure that the top edges and corners are lined up, attach the top face of the box. Use 1-inch screws every 6 inches along the edges to secure it in place. Use 3-1/2-inch screws to hang the house outside. Choose a place at least 15 feet above the ground and away from bright lights, with at least 6 hours of sun exposure each day.