How the hell do you unlock the commercial hub?

The commercial hub now has to be unlocked by expanding the city terriroty. The building is located outside the initial fence line and at a certain point in the tutorial missions after you have trained enough troops you will be able to place an attack on a section to the lower left where the commercial hub building will appear. You need an APC power of 450.

Defeat the zombies overrunning it to unlock the section of land and the building.

Down in your left corner there is three lines. Beside that to the right is an exclamation point, Click that and it shows what you miss to reach level 6.

Good luck

Bwher