Steel construction and building materials

We want to build a very large living space. There will be 10,000 flats in this living area. A total of 50,000 people will live. These buildings will be of steel construction. Doors, windows, floor coverings, kitchen cabinets, bathroom-wc components and everything will be done. Can you find a big company that specializes in both steel and all construction materials? I just want to get advice from Chinese friends on this issue.