4, 2-Gang Boxes (I used Metal, but if you mount to wood, these would work good. Also cheaper at the hardware store) https://amzn.to/2FjwgMv
Other Parts from Hardware Store Metal or Plastic Enclosure #12 awg wire for connecting outlets to relay board #16 awg wire from an old PSU or other device 5v 2amp Power Supply for PI and Relay Board (maybe one for each?)