If you're talking about mine, firstly thanks - otherwise, the design is modular.

Each module is a Gigabyte microATX board with 4 PCIe slots, and 4 GPUs on extenders. This fits in a cube, so there are three cubes in a row on the second shelf of the three-shelf unit.

The top shelf has the middle slat removed to allow hot air out.

The middle shelf has the middle slat removed to install three domestic extractor fans, which blow air UP into the electronic cube modules. The logic boards and GPUs all use extender cables to drop the inputs (ATX 24-pin, ATX12V 4-pin, and all the PCIe 6-pin GPU power cables) down below the second shelf.

The bottom shelf has all three slats intact, and is where the PSUs stand. Each PSU (one per module) stands on its side so it's pulling air in horizontally and blowing air out of the front of the unit. The leftmost module has 3x 5850 and 1x 5830, hence is using an 850W Cooler Master. The middle module has 4x 5830 and is using an 800W Corsair. The rightmost module has 4x 6950 and is using a 1000W Cooler Master.

I want to put in a sub-shelf for the hard drives - currently there's a random piece of MDF board sitting on the PSUs, and the HDs are sat on top of that. However, there's PLENTY of room on the bottom shelf - the middle shelf is somewhat cramped for access but the PSU level is not. It runs surprisingly cool, but is the result of a LOT of R&D (i.e. previous failures, and valuable help from a member of the MMC pool I use).

I'm going to break the habit of a lifetime and actually *finish* this one *completely* before building another one