And the whole thing is set up on top of 2 IKEA lack tables and, at my Mom's back-saving suggestion, pulled out a foot or so from the wall so I can get behind it for easier cleaning access:
Then, to cut the coroplast, I had to first mark out the edges of the plywood, then set the grid fencing on top and mark the inner edges of the grid. Here, the green line is the plywood border, the red line is the inner border of the grid fencing, and the yellow is the cut/score line:
Then I cut and scored the coroplast, folded and taped it into a tray, and viola!
And here it is after a haircut! lol
But I really felt like it still needed some extra height to the grid fencing, and I'm kinda hoping to get youngsters anyway. So I cross-hatched some extra grids around the support grids: