Thoughts on how to fix a depression in the roof

Good news! I have an industrial magnet that is much stronger than the cheap one I originally used. There is indeed metal under the depression. I used the stronger magnet to pull up on the indention and popped it out! It's interesting that the original magnet (one of those that you use to hold photos on your refrigerator ) would not pick up on the metal in the depression but would stick to the metal around it. Anyway, I still might have to reinforce the roof if it oilcans again on me.