Not a bad size... Most are to short.. When I first got into my building you could put a bus in my booth, it was a home made booth and it was really rough so I had to tear it down but to be honest I wish I would have just re-built it in the size it was.. I ended up buying a old binks booth and I always miss my big booth.. You could paint a car in pieces and still have room to do the whole car in the same session..
14' is average width, I think that is the width of my binks.. I would go a little wider if you have the room.. It's unnecessary but it's nice if the space is available.