I am in the process of installing a 10 zone system, with 2 manifold boxes. I already installed one manifold assembly using pvc manifold tees that slip together and have a female thread to accept the valve. I have 5 valves in this box, but added a 6th manifold "elbow" and capped it (for future use if needed).
Getting to the point - I have a six-valve manifold in a rectangular box, however, it is a JUMBO box which measures 18 X 24. Standard boxes are 12 X 18, which is too small for 6 valves, and kind of tight for 5 valves. Cost was $31 from the Professional Supply Store based in Florida (I bought most supplies from them mail order - best prices for most parts). The manifold tees were purchased at a local irrigation supply store, or a plumbing/pump supply store might have them.