In the first Harry Potter book you actually don't know where Professor McGonagall is when she sees Harry catch the Remembrall. She might have seen him from a Hogwarts Castle room like they depict in the movie. In the book Harry catches the memory aid near the ground, in fact he rolls off his broom. The Prof appears almost instantly. In the movie he catches the Remembrall high in the air outside the window Professor McGonagall is seeing him through. Then she has to run through the castle to catch him.
Here's Harry catching the Remembrall. That part came from the HP set Flying Lessons. Harry might have come from there too.
This is the second version of this MOC. I made a smaller one a few years ago. That's it below. I wanted this to be more horizontal and fill the room up more.