I made this for my former cello student, Rachel who is just starting Art College. I've known Rachel since she was 8 years old and she is lovely and is a fine artist.
This is the video I used to make Rachel's bag. I didn't add the loop closure, I just left that part open.
I tried putting a magnet in the flap but it didn't hold to another magnet (I guess the fabric and interfacing was too thick or the magnet just wasn't strong enough) Anyway, the flap was heavy enough (and stiff) to stay down.