The beautiful REK bookcase by Rotterdam-based designer and architect Reiner de Jong is an elegantly designed unit that can be configured to accommodate a book collection of any size with a minimum of wasted space.
The case is actually composed of five discrete parts that fit perfectly together to form a solid block. One, some, or all can be pulled out to accommodate the size of the book collection. At full stretch the REK is a matrix of cubby holes of varying heights (the pieces would not stand freely on their own, requiring each other for support).
The REK stands 202 cm (80 in.) tall, 36 cm (14 in.) deep and at maximum stretch is 228 cm (90 in.) wide.
The bookshelf can be ordered directly from the designer. Prices are available on request, so we expect the REK does not come cheap - and that's before accounting for shipping costs out of the Netherlands.
Source: Reiner de Jong via Boing Boing
I think Dennis\' approach is better: think of it as a generic bookcase where you don\'t need to measure (much) ahead of time. It will fit into whatever space is available (assuming a minimum, of course) ... you won\'t be expanding it later, in most cases.