I make nearly the same design, with this modification---
***I build the end pieces out of standard 8" (net 7 1/2") fenceboard.****
The sides are ply, but building the ends out of fenceboard speeds and simplifies the design.
The end boards are solid, so running a drywall screw or nail to fasten has great holding power. (Nailing to end grain ply is poor practice)
The fence boards are already cut to 7 1/2" width so you don't have to rip to width. Fenceboards are typically 5/8 net thickness, so the length of the sides needs a slight adjustment to maintain bee space. I use 19 7/8" (as standard size) -- this is over bee space by 1/16" but doesn't seem to matter. and makes the components compatible with standard hives.
Tops, bottoms and sides are typically longer rips on the sheet material.
I make tops and bottoms identical -- and drill a cork hole as the entrance in the endboard. The hole is slightly off center (so the opening lines up with the frame gap just below the shoulder of the frames).
Sometimes, I make tops, bottoms and sides same depth (9 3/4")-- this has the advantage of simplification. Tops and bottoms overhang, but I knife notch to receive a line that I use to bind the nuc together. I don't usually nail tops on except for long distance moves. I make the sides out of any sheet good I can scrounge, and the oversize top and bottoms mean that 3/4' material works for sides just as well as thinner stock. All parts are interchangeable. In a pinch, tops and bottoms can be temporarily substituted for sides.
Weakness of using fenceboards is some species (uncured, treated pine especially) will cup. Western cedar/redwood are very stable.