I spent a good while deciding what I wanted and drawing up ideas, and did a final design in Sketchup to give me a rough plan to work to. I decided to include more rack space than I need, and have a sliding shelf for my keyboard so it can be tucked away to save space when I'm just working on edits/mixing. CAD is not one of my strong points, but the design I settled on was this:

The whole thing is made from 18mm MDF, with the odd bit of 2x1 and 3x1 for bracing and as a fixing point for the top. I left a few mm spare on all of the cuts for the panels so they could be clamped together and planed/sanded all together to make sure there was a nice consistent finish.
First panel marked out ready to cut:

Roughed out, and being used as a guide for the next one:


Inside panels with the cut-out for the sliding shelf:

All 4 roughed out and clamped ready for final shaping:

As usual, there's more to come...