No actual knowledge.. But....
1. I assume that there is a roof access in that Building.
2. jumping to lower tiers of roofing is going to be much faster than taking the same stairs and going out of the building.
You are most likely correct, think about it, what is on most roofs ?? Usually A/C equipment, there has to be a way onto the roof from inside the building, if for no other reason than maintenance of equipment installed on the roof. It would be foolish to bring in some type of chairlift machine to life someone onto the roof every time access was needed.
The bigger question is how the shooter knew how to get on the roof from inside the building. Either he had help or he surveilled the building before the event indicating a more involved plot that we currently know.
I think people are getting caught up in the odd conspiracy theories than the bigger issues like who helped him and were larger forces involved instead of a bunch trans and furry kids in a gamer chatroom.
A retired FBI agent was on Fox and he said he could have jimmied the lock leading to the roof and that’s why he had the screwdriver.
Even if that is the case, the roof is usually not accessible to anyone other than maintenance personnel.
After saying that. I must say that a Savings & Loan that I worked at in D.C. in the 1980s, another co-worker & I were able to get onto the roof. I went up only once, and refused to get close to the edge, because there was no protective railing or barrier whatsoever. I never went up there again either. Now I have no idea if someone accidentally left it unlocked or what, but I thought this is not right.
It's been a while but I think it was one of the highest allowable structures at 10 stories max, with the only exception being the Washington Monument.