The glass may be a concern re: sound reflections.
I built a 5'x6' vocal booth and put a small glass window on the door to allow visual contact with the control room.
I ended up putting foam over the glass to eliminate some reflections - and candidly, the visual was not all that important. As long as I can communicate with the vocalists via a talkback mic - I found the window to be more of a negative than positive.
Others may disagree, but when it comes to a small vocal booth (which will likely not have great acoustic properties), I think it's normally better to keep the sound as controlled as possible (in essense, a dead sounding room) with ambiance provided by a processer.
That being said - I would think most building supply stores could provide a large sheet of glass if that's was you really want.