Senior Sergeant Dean Harker said a member of the public alerted police to the incident at the school on Blakes Rd about 2.30am.
He said when police attended there were four youths, all high school age, on a building.
He said their reason for being on the roof was that they were "looking at the stars."
Police will refer the youths to Youth Aid, as they were allegedly unlawfully on property.
The youths, who were from different family bubbles, were also breaking the level 4 lockdown rules.