The whole IMF plan is to drop Hunt through the roof to the gene laboratory. It's not on the ground floor (Ambrose and his men take an elevator up to the lab from the ground floor), but it's pretty definitely deep down (about 40 stories) from the top. But then...at the end of the lab sequence Hunt blows out a wall, and dives out from a pretty considerable height...apparently at least as high as the helicopter was when he jumped, and high enough to use a low-altitude descent parachute.