What I would do: (a) Put the actor infront of a greenscreen, either suspended from ropes and wires (safety expert is probably a good thing) or on a greenscreen covered table. Shoot from the side and from beneath. Use fans to fake the wind against the clothes. Have them flail their arms. (b) Put the camera on a rope, facing down, and lower it from the building to the ground. Or from a crane to the ground. When the image is sped up you'll have the falling person's POV. (c) Reaction shot of someone who saw the splat.

Then when you cut it together you show them going off the building. Then do the shots in order.

So basically (a) should be short cuts to sell the idea that they are falling. (b) is the scary cut that should be the longest is the most likely to actually make the audience 'feel' the terror of the fall. (c) sells the impact without the complications of filming an impact.

RJSchwarz
San Diego, CA