Headquarter

The headquarters is the main building that allows you to upgrade all of your other buildings. When you start, you can work on 2 buildings to upgrade at a time. The higher your VIP, the more buildings you can upgrade at once.

I recommend that you work on your headquarter all of the time until you can reach your player level, then start working on other main buildings like shipyard.

Your second can be used to upgrade each of your factories.