I made this small version as a tester, and was really happy with it.
If you watch the video the following steps will be easy to understand.
Step 1: Glue and nail the boards together
Step 2: Find the center and draw a line using a 'compass'.
Step 3: Cut out the circle. I used a jigsaw.
Step 4: (not pictured) Route out a spot on the back for the clock kit to fit into.
Step 5: Paint! I printed a clock face off the internet. The easier, faster way would be vinyl.