Whether you have pet ducks or a few wild mallards have found your yard and decided to stay, you can build a duck house to keep them safe from predators and provide a safe nesting spot. Domestic ducks rarely fly, so the time to build their house is before their wild peers fly south for the winter.
Cut six 1-by-12 boards, 3 feet long. These will serve as the sides and the back of your wooden duck house. Since ducks have no fighting defenses and domestic ducks rarely fly, they are literally "sitting ducks" for predatory animals to target. Therefore, the safest place for a duck house is in the water.
Use one piece of the plastic composite sheeting as the bottom of the duck house and another piece for the top. You may substitute regular waterproof plywood for the top panel to save money.
Attach the first row of 1-by-12 wood boards, cut to 3-foot pieces, to the bottom panel with screws. Do this by inserting the screws from the bottom side of the panel into the board when the entire thing is upside down.
Cut two more 1-by-12 boards 2 feet long and use one of them along the front side to make the front wall. There will be a 12-inch opening for the ducks to enter the house. Any wider, and they may not feel secure enough to nest; any narrower, and they may not attempt to enter the house.
Insert one of the 2-by-2 boards in each of the three corners of the box and the other two along the inside edges and attach with galvanized screws from the outside. The boards will extend 1 foot higher than the bottom row, but that's fine.
Screw the next row of 1-by-12 wood boards on top of the bottom row of boards, using the support boards to screw into from the outside.
Place the last panel on top of the side walls, but slide it forward so the back of the panel meets the back side wall. This will look uneven and funky in front, but a duck's natural habitat is under overhanging branches along the sides of ponds, so it will feel natural to them. In addition, it allows you to install hinges along the top back side of the panel, attaching it to the back wall. Use galvanized screws to attach the hinges.
Insert one or two thin nails in the top front of the roof panel, just above the front wall, to hold the panels in place until you need to clean the duck house.
Add ballast to the bottom. This can be anything you have handy: a cinderblock or a bag of sand attached to the bottom of the duck house by a rope. The ballast will allow the duck house to move up and down with the water but not float to either side of the pond.