Now that you've decided on your layout, glue the pieces to the 24x24" piece you set aside earlier. Line up along one edge working left to right, row by row. The end piece scraps from earlier, work perfect to finish the pattern.
I use big books to flatten and clamp down pieces as I go while the glue dries.
If there are small gaps or spaces, don't fret! I've got a tip you'll use later to fix this.
Now would be a good time to paint and distress the 8 ft piece of lumber for the sides.