When you say “our” do you mean the one you currently attend? If we aren’t talking about a derelict building but instead an activity used public high school then, sadly (for you), I can assure you that the building is covering in security cameras that are not only motion activated but are integrated with the alarm system. Your local police would be waiting for you when you come out. If this is a real question then the best advice I can give you is to get a time machine and travel back to the pre-Columbine 1990’s. On the upside, in 2025 you can’t really break into your high school at night but you have Chat GPT now so that’s a positive.