Dry erase boards: glass vs. white board
When I was a grad student, I mounted a 1x2 meters glass plane in front of a white wall at my place. It was great for scribbling stuff and for large drawings. I also developed the habit of drawing on the glass doors at my previous lab, because the closest whiteboard was in another room.

The big advantage: glass is very smooth, you will never have stains accumulating like on a white board. No matter how zealous you or the cleaning staff is, white boards are a bit porous and the material deteriorates with time (UV radiations, etc.) and becomes even more porous, making it harder to clean up. 
For the same reasons, if you inadvertently use a permanent marker instead of a white board marker, it's easy to clean it up. Finally, existing glass structures also provide large surfaces for drawing. 

The disadvantages: lighting (back lighting, shadows, etc.) can impede reading what you wrote. It helps if the glass is placed immediately in front of a white wall. Also, the cleaning staff might erase your brilliant ideas overnight because they were instructed to clean all windows.