Sand the piece of wood so that it's smooth. Wipe any dust off the wood.
Paint the wood in your choice of colors. Allow it to dry overnight or for at least a few hours.
Position the four wheels on the four corners of the underside of the wood. Place the screws into the holes in the wheels and drill or screw into place. Flip the wheeled wood board right side up.
Attach one 48-inch pipe to the shorter pipe using a 90-degree elbow. Attach the other 48-inch pipe to the other side of the shorter pipe using the second elbow. Screw the flanges onto the open ends of the 48-inch pipes.
Paint the pipes to match the wood, or leave the pipes unpainted if you prefer the industrial look. If you choose to paint them, you may need to use a primer first if the paint does not adhere to the pipes. Let the pipes dry for several hours.
Position the flanges on the top of the wood board so that they are in the center of the board on each short side. Screw the flange on the right side of the board into place, then make sure the pipe is even and level before screwing the left-side flange in place. Place a few hangers on the rack.