This is the simplest build ever.
All you need is 1X2 boards.
I measured how tall I wanted the faux headboard to be and we cut two boards to that length for the sides of the headboards (width of the bed).
We then added a 1X2 on the top, connecting the two boards and then one on the bottom where a headboard should end (about where the height of the bed).
Next, we cut three more 1X2s to fit in the middle of the boards going vertical, spacing them each apart equally.
We used a brad nails and nails to hold the boards to the wall. Then we caulked and painted.