Cut your plywood backing to 14 3/4" x 24".
Use a straight edge to find the center of your plywood backing. Create four even rectangles to help map out your design.
Cut a scrap piece of 1x3 at 45 degrees to use as a stencil for your mat holder. Use this stencil to trace your design.
Start each board with a 45 degree cut. Line up each board with the design you traced. Once lined up, use a pencil to trace the cut mark on each board. This will be where the 1x3 overhangs the plywood backing.
Cut your 1x3's on the cut lines. All cuts will be made at 45 degrees.
Attach all 1x3 boards with a brad nailer and 1" nails.
Cut four pieces for your border (2 long edges @ 24" and 2 short edges @ 15 1/4"). Attach them to the mat holder with a brad nailer and 1" nails.
Attach large hooks on the front for the mat and small hooks on the back for hanging.