While fireplaces accentuate the largeness of a room, the rooms do not all come in one size. For smaller rooms, like a child's bedroom, fireplaces were sometimes built in the corner of the room to exploit the space there. In fact, it is now easier to install a new fire place in the corner of a room because the fireplace walls could be tapered exactly just so in order to reflect the heat more efficiently into the room.
Most fireplace glass doors are made of tempered glass with either ceramic or anodized aluminum frames. Glass is placed on the door so that the fire can still be appreciated even with the door closed. Most of these fireplace doors can be bought stock - meaning that most of the door that are for sale can be purchased off the rack and installed with minimal changes.