I didn't know it could be done with PVC. The plenum pipe must be fairly large.
The plenum was actually a box approximately 32 " high and sized to fit the top of the A coil . Made from some high temp plastic , double walled with insulation pre-installed . Used a very large adjustable hole saw to make the starter holes . Don't remember all of the details re sizing , seems the largest pipe was 10" . Kind of pricey , but it was what the customer wanted . All modern down flow systems , where the duct work is under the slab are done in PVC . The only real difference was the need to insulate the pipe in my example . Just used regular fiberglass wrap , stapled and zip tied on .
Dusty