I mean, what are the free dark figures doing on the roof of the high building and what is the rationale behind? Seems that the main character is about to take a risky jump from the high building, but why this would be required? Suicide seems unreasonable at this point and does not explain why to take also the Apple together, this would neither hide nor destroy it reliably. The scene may be understood as metaphorical. Is this the only explanation?
The characters are probably about to perform the Leap of Faith. This is a strong symbolic acrobatic move in the Assassin's Creed mythology. In the game Assassin's Creed 2 it is revealed that completing this manoeuvre is required as part of the initiation to the creed. The movie is most likely using this to show that Cal has now fully joined the creed and is devoted to stopping the Templars.
More can be found on the game's wikia: http://assassinscreed.wikia.com/wiki/Leap_of_Faith