Use a measuring tape to acquire the length and width of the basement door opening.
Mark the measurements on the wood of your choice using a pencil or wood marker.
Cut the wood to fit the measurements carefully using a circular saw. Wear safety goggles to protect your eyes.
Use a wood planer to plane the newly cut wood to adjust the thickness of the door to your liking.
Load a drill with a hole saw bit and create a hole through the door at 36 inches high and 2 3/4 inches in from the right side edge. This is the hole in which the door knob will be installed. Switch out the bit with a paddle bit to create the door's latch opening, on the side of the door at the same height as the door knob hole.
Sand the entire surface of the door thoroughly with fine-grit sandpaper.
Wipe any excess saw dust away using a soft cloth.
Apply a coat of wood stain to the door according to the specific brand's instructions. Allow the door to dry completely before using.