Most of our "1/2-inch" plywood isn't 1/2", but rather 15/32", or 11.9 mm. If you're building from scratch, it seems overly optimistic to cut every single piece to precise pre-defined sizes rather than planning on doing some final fitting or trimming. IME, anyway.Did you try this? 1/2 inch ply is 12.7mm thick. Metric ply is 12mm thick. If one does as you suggest the parts won't fit together properly. Try it. Post pictures. Good luck.