China fabricates 20-foot office buildings by modifying standard shipping containers, creating prefabricated, modular spaces that can be quickly assembled on-site. These buildings are constructed off-site in factories and are designed to be durable, insulated, and customizable, with options for interior layouts, windows, and finishes. The process leverages China's manufacturing capacity and expertise in steel structure and prefabrication, resulting in cost-effective and flexible office solutions suitable for various temporary or long-term needs.