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.
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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.