Of course you can build shelves in your alcoves but that will cost the same as buying these (at least) and you can’t take them with you when you move. In addition to that, these have graduated shelves so you could put those bigger books at the bottom and keep the paperbacks above, or use them for display purposes as they have done here. For those of you with an alcove waiting to be filled the measurements are 180 x 96 x 35cm. For those without, or, more likely with an alcove that is the wrong size, they would look just as good propped up against a wall.
365 Objects Of Design, Stylish Storage