For me, it'd have to be a wonderful friend who lives in America. I'd cross an ocean for her. I'd try to mimic Jesus, but even he didn't walk across the entire Atlantic. Therefore, until I get a plane ticket, I'm boned. So plank it is.
Of course, the real smartarse answer if no-one's said it already, is to go down the lift that brought you to the roof in the first place and go up the lift in the other one. >.> If that's not an acceptable answer (it isn't), plank, definitely. I'm scared of heights without a barrier, but I'd find some way to get across if it was the last thing I ever did (and unless it's the Matrix, it would be).