Here is a basic drawing of a case deign that I think would work quite well. I have visions of getting a basic ATX case and stripping it down and making new sides out of curved sheet mild steel. Painted in a Kawasaki green. The optical drives I want to be like the Packard Bell ones, where you have the desired panel on the front and hinge it so that you can still open it through the outside.
A second thought of what I have just seen to to put the case on large casters and have the air going straight in at the front. like this
If it's going to be a Water Cooling case, then cooling source is done. Now it's just the design and the way it looks, which is up to you! You're the one that will be using/ looking at it for the majority of the time, unless you're going to sell it; if this is the case, you will have to make sure it is appealing and not an eye soar
I'm just waiting to sell my current computer and building another computer and I'm buying a cheap case and modifying it.