This is all just a design exercise, but it’s a rather beautiful one. How do you put 4 GTX 295’s in a motherboard? How to do combine 9 motherboards into one big disk? How do you stack 6 disks and cool them all? How do you combine 10 stacks?
This isn’t a practical design for a variety of reasons. But it’s great fun to study.
And this is not entirely theoretical. He actually homebuilt his own CPU cluster in an Ikea cabinet.
The best home-built GPU cluster I know is the impressive 110-GPU Atlas.