This picture shows the pre manufactured aluminum recessed shower can or pan. This item is designed to fit in between standard wall stud distances, and wall depth. They simply nail to the studs and are ready for the tile over process to come.
The surface facing us is specially treated with a coating that will help the tile adhesives to stick. If the aluminum were left bare, the tiles would not stick for long, so this coating is needed - don't try to make your own box.
That's not to say that you can't build your own recessed shower shampoo box from wood framing - that will work just fine - you just wouldn't want to apply tile directly to the untreated metal material.