Open rig ingredients:
6 PCI slot ASrock H81 Pro BTC motherboard
http://www.asrock.com/mb/intel/h81%20pro%20btc/
1 Intel SSD
2 DDR3 Memory sticks each 4GB
Seasonic 1000W platinum PSU powering everything except 1 TITAN
Addidional 650W Seasonic PSU for the TITAN
PSU cable that starts second PSU when computer starts
Switch to start the computer
Cheapest Celeron CPU you can find
5 PCI 16x to 1X cables
UTP cable to connect to main computer
all together this costs around 750 EUR
I was thinking about buying a second Netstor box when this open rig came into perspective so I thought I'd try this first and see how it goes. It goes great ! Compared to 1500 EUR the Netsor box costs it is a bargain.
The penalty is that it takes a couple of seconds or a fractions of a second to upload data to the network nodes. But in my case, since I already have one Netstor box connected, it doesn't make sense to buy a second Netstor box since Windows can only handle 8 GPUs in one system so this 2nd Netstor would be a network node also.
The rest is pretty much as glimpse explained. 3 Titans in the main box and 4 in Netstor.
Mother in the main box is ASUS Z9PE-D8 WS
http://www.asus.com/Motherboards/Z9PED8_WS/
with 2 Intel E5-2687W CPUs. 32 GB RAM
As for the GPUs, I think the best ones for openrig systems is ASUS 780 6GB Strix, they are much larger because of their oversized coolers so they might not fit sandwiched in a normal case, but for open rigs they are perfect. Their coolers are so cool that they don't even start spinning when you power on the computer. Only after 15 - 30 seconds of Octane rendering it starts to spin. This cooler is far superior to stock TITAN coolers and the rendering speeds are about the same. Not to mention 780 is much cheaper.
I have also replaced stock Netstor PSU for Seasonic because the stock was very noisy. I always use Seasonic because they are very silent and they seem to be reliable.
Also there was a small fan on the chipset inside Netstor, I just pulled it out becuase again it annoyed me. Works well without it.