[STEP 1] Start with a 12-foot plank of 1×10 lumber--cedar is best; pine will work. Cut it to the lengths shown at right.
[STEP 2] On the outer face of the front, cut an oval-shaped entry hole, 4 ½ inches wide and 3 ½ inches high. Then turn the board over, and starting just below the hole, score the interior face with shallow horizontal cuts about 1 inch apart. These will give ducklings a toe-hold for climbing out of the box.
[STEP 3] Attach the side piece with four 1 5/8-inch wood screws driven through the back as shown. The back should extend beyond the side by 3 inches on top and bottom.
[STEP 4] Using a ½-inch bit, drill five holes in the floor for drainage. Attach the floor with two screws through the back and two through the side. Then attach the front to the side and floor.
[STEP 5] Bevel the top outer edge of the door, or round it with a sander or file. Then attach the door at the top only with one screw through the front board and one through the back. These screws will act as hinges, allowing the door to swing open. Drill a small hole through the bottom right of the front piece and into the side of the door. Insert a nail of a slightly smaller diameter to pin the door shut.
[STEP 6] Attach the roof to the back, side, and front.
[STEP 7] Finally, put 6 inches of wood shavings (not sawdust) in the bottom and place the box directly above the water or along the water's edge by fixing it to a tree or a metal pole. A conical metal flange or other predator guard is a good idea (see ducks.org/ conservation/duck_box_plans.pdf). Keep the box at a height you can reach, say 5 feet, as you will need to replace the wood shavings yearly.