I wish I could remember. See my article here:
http://www.uer.ca/....asp?storyid=10581... where I was on the roof as well.
Likely it was the intertwined staircase that went up to the roof exit. You have to jump over from the normal one to the alternate universe one over the railing.
There are a lot more security cams around since the late 70s. Security is farmed out to grumpy-'r'-us types who would yell at you for walking around the top floor of the parking garage with a camera.