This is a pattern to make a rack capable of holding 5 Raspberry Pi type B+ or B 2 with a child card Hifiberry Amp + on each. An opening on the side allows access to the terminal blocks for power and audio cables, and a front opening provides access to the Ethernet ports. A compartment on the side can accommodate an ethernet switch.
The second model adds two additional locations because I needed 7 location, but my printer tray was too small.
See picture for more comprehension.
Full multiroom presentation available here (in french): http://www.maison-et-domotique.com/56929-realisation-de-multiroom-audio-a-base-de-raspberry-pi-hifiberry/
I generated gcode with Slic3r and all worked fine.