Did you know IKEA.....

........apparently does NOT manufacture flat pack furniture itself. Its famous BILLY bookcases are manufactured at the sprawling independent company Gyllensvaans Möbler in Kattilstorp Sweden.

According to the video, Gyllensvaans manufacturers flat pack furniture for stores and warehouses all over the world. The trend seems to be toward the vast automated factory which can produce multiple product lines for multiple companies In the case of the designer of builtins for the multifamily apartment, the design can be outsourced for manufacturing at large job-lot factories then shipped directly to the multifamily apartment complex and stored in a temporary on site warehouse / shop. The savvy all builtins designer might find it possible to both outsource production and subcontract installation, the better to keep it lean and green :)