After the previous build server setup had destroyed itself with fire, much like the Phoenix from the Ashes, I decided to reincarnate it in a slightly more resilient (read non-flammable) case.
The king is dead, long live the king:
I used an Extended-ATX case with a dead motherboard I had lying around, and put all the boards and the hard drives in it. There is also an 8-Port Ethernet switch that connects to all the boards and means there is only 1 Ethernet coming out of the box.
The boards and the switch are mounted to a laser-cut acrylic panel I made in Onshape. The hard drives are securely mounted into the rails on the case for them.
Closeup with SATA cables removed:
I have also upgraded all the builders to Ubuntu 16.04, running buildbot-ros to build packages for ROS Kinetic.