My design is based on that of kentdvm http://www.instructables.com/id/Making-Carpenter-Bee-Traps/, see his project for construction tips. His trap is hung like a lantern and has an overhanging roof. Mine needed to be attached directly to the wooden overhang of my house, high above the ground, so it did not need its own roof, but it did need to be emptied by someone standing on the ground far below. I did not have weathered wood for making the trap, so I used ordinary lumber, on the theory that the bee is lured not by the trap's wood so much as by the pre-made holes. My design for a smaller trap will appear as its own Instructable as soon as it proves it will catch bees.
Any carpenter bee trap will be more effective if the bee-made holes in the protected structure are plugged. I use a color-matching outdoor caulk.
Step 1: Plastic Parts From the Grocery Store
The clear plastic funnel is cut from a Dasani brand drinking water bottle, chosen because it has a unique pinched waist ("rest mark") that secures the funnel in the trap.