"The dimensions of the case are: depth - 680mm, width - 230mm, height - 620mm"

I'm building my own custom chassis although mine will have these dimensions: depth 620mm, width ~230mm, height 650mm. These may change some cm here or there. I'm building a prototype in cardboard because I ain't that good with sketchup :\

Anyway the prototype is almost done and it is freaking HUGE. My current chassis (p182) looks like a miniature model of a chassis if I compare them! I'm seriously considering scaling it down or changing design to a cube. Although cubes are ugly as hell when compared to a tower... yeek (IMO ofc)

I'm going with a similar design as you but with the top compartment dedicated for hdds, psu, fancontrollers etc. And that compartment will be isolated from the others and only have a 120mm fan blowing air through. And then a vertical 360rad up the front and another 360rad in the lower compartment. And dual loops.

Do you have thoughts of scaling it down?