I can give you a much easier method for a dry erase board. Go to the local Lowe's/Home Depot/DIY store and buy a sheet of "Tile Board". It's used to make cheap showers and bath enclosures. Thus it is white, waterproof and most of all cheap. I bought a 4ft x 8ft sheet last year for less than $10. I glued some flattened tin siding to the back and presto instant mangentic whiteboard for under $20 and an afternoon's work.

I'm currently working on using "line tape" which is similar to pinstriping tape to mark off a grid. I just can't seem to find it in a light gray to avoid it contrasting too much.