The 1/2 pre-finished plywood works great here. Working with polyurathane glue is a bit harder than wood glue, since there is no "tack" to it, and it takes a few hours to dry. I re-enforced all the joints with 3/4" x 3/4" wood strips on the blind sides, which will act as supports for shims on the tops of cabinets and nailers for the trim on the bottoms.
Here is the front part of the upper corner cabinet:
I designed this cabinet to be only 10 inches deep on the sides instead of the standard 12. This changes the backs from 27 to 24.5 inches, allowing a full 48 inch wide window with trim. It also makes the back corner under the cabinet more visible.
This cabinet will hold a couple of "D" shaped lazy suzans that use almost the entire footprint.