You could make the chopper get over the building like this :
YourChopper move [X,Y,Z]
or
YourChopper move getpos "Name Of A game Logic On The Building"
Then you could have the chopper fly low.
YourChopper flyinheight 10-20
Adjust the hight to your suits.
You may need to make the chopper careless and combatmode blue.
YourChopper setcombatmode "Blue"
YourChopper setbehaviour "careless"
Does this help ?