Details to build your own here : http://www.thingiverse.com/thing:236092

For the hardware I used :

1x seasonic 1250W 80+ Gold power supply,
4x Gigabyte R9 280x (should fit other models),
1x ASRock 970 Extreme4 motherboard,
1x AMD Sempron 145 CPU,
1x Kingston HyperX 4Gb DDR3 1600 MHz RAM,
1x Sandisk SSD 64Gb,
1x 200mm NXZT fan,
1x 120mm Noctua fan,
3x 16x-16x PCI-E risers,
1x 1x-16x powered PCI-E riser

I can acheive 2.9 MH/s with cgs undervolted to 1075mV, sgminer 4.0.0, optimized .cl for cgminer, 8191 TC (yes 91 not 92), 1055/1500.