How many building levels (expansion levels) are there?

The buildings within your base station can be upgraded. With each level expansion of your factories the amount of production increases.

The following expansion stages are available for your buildings:

Steel factory
-> 15 levels
Carbon factory
-> 15 levels
Cement factory
-> 15 levels
Fuel factory
-> 15 levels
Military Headquarters
-> 10 levels
Economics Centre
-> 10 levels