Here is a simplified drawing showing the side elevation.
I have omitted the interior details for clarity so don't panic.
From theses basic drawings we can derive basic panel sizes and router cut outs and rebates.
Ian
Edit Note: I just realised there is a bit of an assembly issue this this drawing. Guess what is it? I will re draw this diagram tonight.
To make clamping the top , bottom and sides together easier I have re arranged the side joint so the top and bottom rebate into the sides. This way shorter and no doubt more accessable bar clamps can be used.