How do I get on the roof?

Hint 1 of 7:

First, get into the gym.

Hint 2 of 7:

Do you see something that could lead to the roof?

Hint 3 of 7:

Yes, the ladder in the upper-left corner!!

Hint 4 of 7:

But you can't reach it.

Hint 5 of 7:

Think trampoline.