Generally the number of variations is large enough that you cannot build standard products and then select from inventory when a customer orders a product. Instead, the product must generally be built for a particular customer to his or her specifications. Today, a customer can go to a custom furniture builder and have virtually anything built. These companies exist and, for a price, they will custom build anything you want. If however, you don't want to pay the high custom price, you are forced to choose from furniture pieces that are being offered by the major mass builders of furniture.
Prices are much less but selection is more limited.
Technology is about to change this. This means, without paying the high price for a completely custom product, the consumer can still have a product customized for their needs or wants. In addition, these custom products can be obtained in a relatively short period of time. These ideas are already becoming available for many products. Recently I saw an ad where a well known maker of tennis shoes were willing to custom make special shoes, with custom color combinations and a monogram for only a small additional charge over their normal retail price.