In order to free fall you must first be on top of a building. Just run or walk off and you should form a diving position. If you were high enough, the game should shake and you can see the speed. You can do this with the construction worker
that you were supposed to "save" from falling off of the building, but when you land you will just roll and the construction worker will not be affected. Note: Sometime when you free fall you will lose health if you hit the ground head on.