Do you like to open and close your windows often? If so you'll need room to swing back the shutters to access the opening mechanism of your window. Instead of having very large ones, you'd be best to go with a pair of shutters over a large window in that case. Otherwise, if you want maximum visibility of your view, go for as few shutters as possible and the widest blade spacing. Without seeing your room, I'm afraid I can only give vague advice! There will be a lot of light leakage around the blades, so the room will not be very dark for use as a second bedroom.