Especially if it were a Saturday and the building/front door was shut and closed.
Gunman identified as video shows body and rifle on roof after Trump shooting
UPDATE: This image appears to show a ladder behind the trees, and the inference is the assassin used it to get onto the roof. This raises the question of who owned the ladder, and how did it get there? Did the assassin drive it there on a car of some sort, or was it placed there for him?
615 Whitestown Rd, Meridian, PA, 16001.
No Minister 
It’s a single storey building, anybody with basic parkour skills could use the window frames to get up.
Crooks. A register Republican supposedly but on record as donating to Democrat aligned fundraisers… Hmmm.
The stench of patsy rises higher with this guy.
https://www.nzherald.co.nz/world/donald-trump-shooting-heres-what-we-know-about-thomas-matthew-crooks-the-suspected-trump-rally-shooter/H3BU73DO5NBZNJ364G5TFSEGGM/
Most info in one link…
https://www.malone.news/p/a-psywar-assassination-attempt?
In the light of recent DoJ actions over partisan political attempts to derail the current Republican front runner, I am seriously doubting the Secret Service now headed by an ex Pepsi executive lady with zero experience in security work performed with the absolute commitment historically attributed to such state employees.
I am not being sexist but expecting a DEI employee to do what was traditionally a macho male task is fanciful in the extreme and to have a building roof so close to a stage where it was no state secret the most widely despised by so many was to speak, left unoccupied defies every tenet we have been led to believe was Standard Operational Process.
If ordinary people on the ground could observe a person in camouflage carrying clearly a weapon crawling into position for a shooting yet at least two security persons with weapons in an elevated site did not see in the clear leads me, a long standing denier, to believe the very worst in thinking this was a state sanctioned assassination.
Will yet another conspiracy theory be proven accurate, the desperation is palpable in my mind.
The current head of the US Secret Service is an ex field agent in the Service, joined in 1995.
https://www.secretservice.gov/about/leadership/director
So she knows how the service operates….
Not only that but how the hell did he keep crawling up the roof, with a clearly visible rifle, while people are pointing at him and calling out, some to cops, some to their friends. One guy timed that video: