For a good ergonomic posture and really to help your eyes travel from one screen to the next, the two screens should be roughly at the same height.
Using a miter saw, cut the 1×4 and the 1×3 board per the cut list.
Start by attaching one 1″ x 3″ board to the 1″ x 4″ board at a right angle using wood glue and finish nails.
Layout and attach the rest of the 1″ x 3″ boards with ¾” spacing between them.
Attach the second 1″ x4″ board to the other end of the 1″ x 3″ boards using wood glue and finish nails