Rob Johnstone: Either birch or red oak plywood will do the job nicely. They are quite different in their appearance, so I would select the one that I liked to look at the most. If you are going to paint the desk rather than use a stain/clear finish of some sort, I recommend the birch. The red oak’s open grain makes painting just a bit more challenging. As to the poplar edging on the plywood, once again it will be sufficiently durable, but it will look very different from the plywood. (Less so on birch, but even there it will be significant.) Again, if you are painting this piece, that makes absolutely no difference. If you are planning on staining and or applying just a clear finish (like a wipe-on polyurethane for example), I would recommend attaching an edging of the same species of wood as the plywood you are using. In my opinion, that would look better. Hope this helps.