Peter's own quick thinking helps him survive. He could use his surroundings during the fall. For example, if there are ledges on the building, he can use them to break his fall. He can also calculate the best way to land, using his acrobatic skills that come with his powers, so that he minimizes the damage to himself.
One possible reason could be to save someone. Maybe there was a threat in the building that he could only stop by jumping off and using his powers in mid - air. For example, a bomb was about to go off and the only way to defuse it was to jump from a certain angle.
Perhaps in this fanfiction, Peter has some new power or gadget that he's testing. So when he jumps off the building, instead of the usual web - swinging, he activates this new ability which allows him to fly or at least glide to the ground in a very cool and unexpected way.
One possibility could be that Peter is extremely stressed at school. Maybe he's being bullied or facing overwhelming academic pressure. So, in a moment of despair, he jumps off the school roof. But then, he could miraculously survive and this event could be a turning point for him to face his problems and seek help.
His best friend could be a main character. This friend might be the one who tries to understand why Peter did it and be there for him during his recovery if he survives. Maybe the friend was the only one who knew Peter was struggling before the jump.
He could be trying to save someone. Maybe a civilian is falling from a higher floor, and Peter jumps off to catch them and use his webs to swing them to safety.
One great fanfiction is 'Peter Parker: The Avenger's Secret Weapon'. In this story, Peter uses his intelligence and spidey - sense to help the Avengers in unexpected ways. It has a lot of action scenes and great character interactions.
In fanfiction, if Naruto jumps off a cliff, he might be saved by a hidden power. Maybe he discovers a new jutsu on the way down that allows him to fly or slow his fall. It could also be that a mysterious character appears out of nowhere and catches him.
Yes, there might be. You can check fanfiction websites like Archive of Our Own or FanFiction.net. Just search for 'Peter loves ducks' within the Avengers fanfiction section on those sites.