How the heck do you get to the rooftop? I tried the elevator but it won't let me out onto any of the floors. Tried hj'ing from the roof of the adjacent building (wearing TinCan's headgear w/ lvl 50 hj) and still can't get there. What's the trick?

It's floor 80. The panel only shows 20 floors, you need to flip panels (there's a button on the right bottom corner).

Hmm. I did flip a panel but only saw that it went to 40. I'll check it again. Thx bud.

keep pressing it.  press it once it will change from 1 - 20 to 21 - 40.  press it twice it will go to 41 - 60. press it again and you should have 61 -80.  hit 80...follow the stairs....and jump down

You can also HJ to the roof from the bridge next to the building..... >.>

Wearing Searaphim's and Tin Can's Headgear help too if you want to HJ up there.