I thought I would share my 8 GPU rig design. The 8 GPUs are mounted vertically in a frame of total size 50cm x 50cm x 35cm. In theory, there is room to mount up to 14 GPUs but I'm happy with just 8 in each rig. The one on the left with it's guts hanging out is the prototype. (One of these days I should shut it down and tidy up the cabling)
The overall size and dimension allows for easy pickup and carry and I suspect the extra space between each card allows them to run a little cooler. Single 1500 watt Silverstone titanium power supply in each along with an ASUS Z270-A motherboard, 120GB M.2 hard drive, 8GB ram, running windows 10 pro. GPUs are GIGABYTE 1070's in the first rig, 1070ti's in the 2nd.