I went with wood, currently holding 4x 1080ti & 4x 1070. I have 4 AMD cards en route, and 3 more nvidia ti's here. I'm having second thoughts about adding AMD to the mix, but we'll see how the config goes. I'm 2 weeks in with 8 cards, plug and play, except that I had to plug all 8 Nvidia into the bottom pcie slots as someone around here suggested.
It's 36" long overall with a 35" bronze closet bar (Lowes) to bolt the cards to, a wood rod for riser support, oak plywood, and a metal mobo tray. I'll add 2 more cross beams under the oak plywood and a few more screws to transport it.
http://comp49.com/asus.jpghttp://comp49.com/asus2.jpgMark off your first 8' 1x2: 36", 2x 7", 2x 11", 2x 11.75", approx no waste. Mark next 8' 1x2: 36", 2x 12.5", and you're left with ~35" piece for under risers. Wood cost $3, oak plywood $6, closet bar $4. You need 1 1/4" screws and I paid $1 for the wood rod. If I did it again I would actually use wood glue instead of staring at the bottle the whole time.
Metal would be better, but this took me 2 hours max.
