Determine how long you want the overall frame to be and cut the sides to that length.
Once all four sides are cut, make these 45º corner pieces that the canvas will attach to. We found some scrap wood in the garage and ripped the thickness down to 1/2″ with a table saw.
Attaching the corner braces was a little tricker since the edge had to be perfectly flush with the frame, and we couldn’t find a hard surface for it to sit on that was exactly the right height but we got there!!
Next, stain or paint your wood as desired I gave mine a light coat of Minwax Driftwood, which is mostly transparent but gives it just a hint of color and makes it look more finished.