Made of solid 1x12 (3/4 ” x 11 5/8”) the bottom measures 29 ¼” inches and the top 34 ¾” inches. These measurements are for the outside or aft side of the transom. That way if you decide to make your transom of thinner or thicker stock it will still be right. The aft, or outside dimensions remain the same.  The angle is 13 degrees. Or 103 degrees for most circular saws, since your adding 13 to 90. Remember to mark the center clearly on top and bottom edges. This is crucial for alignment later.

The arched crown addition is optional. (Looks sweet though.) The transom could also be made from ½” or 3/4” ply if you have it. My first Summer Breeze transom was made from 2 x 12 stock. Which seemed to be overkill, however Scott Widmier used 2 layers of 3/4" ply laminated for his boat.