Place the two 1-by-12-by-16-inch hardwood boards parallel to each other on a work surface with the 1-by-16-inch edges resting flat. Orient the boards vertically. Space them 28 inches apart, measuring from the outside edges. These are the leg boards.
Butt the two 1-by-12-by-28-inch boards against the top and bottom 1-by-12-inch ends of the leg boards to form a rectangular box assembly. The 1-by-28-inch edges should rest flat on the work surface. These are the seat and bottom support boards.
Use a screw gun to drive four evenly spaced trim head wood screws through the seat and bottom support boards into the ends of the leg boards where they join together.
Brush two even coats of wood finish onto the entire window bench using a paintbrush. Allow the paint to dry at least four hours between coats. Wait 24 hours after the final coat before you handle the assembly.