Find a better Location:
In the game, you will find a different house in which you can go to the roof by using stairs, but there are also some houses which don't have any stairs, but you can still go on their roof.
For example, you are on the terrace of a squad house. You will see a door and a shade upon it. Try to jump and climb on to the shade and then to the roof. The process is simple once you get the hang of it.
Using this trick will help you get at a higher location where the enemy won't expect you at all, and you will be able to kill them, or you can find the enemy's location from the roof.