With 1u vertical spacing and 0.5u horizontal spacing, there are lots of existing keyboards out there with the same layout.
I once took a Chicony keyboard with that exact layout, modified a Cherry G80-3000 case and put it in there. Mind you, the Cherry case was not prepped for the plate so most of the work was cutting the borders.
Other than that, I think that laser-cut plywood or MDF > plastic.