my black-city has like no buildings but my friend's has a lot what's with this?
That's because all your people left from being bored from the city. Go to the Entralink, connect to a White, and visit a White Forest and talk to people. They might head to your Black. When they do, buildings will sprout again.
It's because you don't have as many people in yours. Connect with your friend and get a bigger population, now! XP But seriously, to fix that, trade some people over.