Measure the width of your bed to get the total width for the homemade headboard. Mark the height you want the headboard to be, adding a few extra inches so you are able to mount the bottom edge below the mattress. This keeps it from showing.
Cut the beadboard to size for the headboard. You will likely need to use two separate pieces as beadboard usually comes in 4-feet-by-8-feet sheets. To keep the grooves going vertically, you'll need to butt two pieces side-by-side for most beds.
Cut the 1-inch-by-4-inch boards in lengths to create a frame around the headboard. Nail the pieces together to create a rectangular headboard frame. Drill holes on the back side for "L" brackets to reinforce the headboard frame structure.
Lay the headboard frame down on the floor with the back side facing up. Lay the beadboard on top of it with the grooved side that you want to show facing down toward the floor and frame.
Nail the beadboard into place using finishing nails. Slide the two pieces of beadboard as close as possible to reduce the crack between the two. Add a narrow piece of wood down the middle of the frame to cover the crack if desired.
Paint or stain the beadboard headboard. Choose colors that coordinate with other furniture finishes in the room.
Drill holes into the headboard to prepare for the screws. Screw the headboard to the wall above the bed, positioning the bottom of the headboard frame so it is hidden by the mattress. Cover the screws with wood plugs.