Somewhat like Umineko

There are two people in the building after he regained consciousness

-Also, his last memory was unlocking the door?
He's trying to escape right?

-Repeat this in red: The guy unlocked the door to the rooftop, before he went through the door to get onto the rooftop.
The door is not locked before going to the rooftop

-Also repeat this in red: The girl is making the pipes fly in the air at the guy.
DENIED.

Are the pipes that hit the guy still on the rooftop?

Those pipes that hit the guy are still there

I think I got this then. Though if we make our deductions in blue and get it wrong, we can't post again until the next story? Or can we make as many deductions as it takes?

You can still post your deductions even if it's wrong, there's no time limit either
You can submit all your deductions, the more the better

Okay then, here goes.

The guy goes up to the rooftop after he got done with P.E. He goes through the door to see the girl up there, and pipes coming at him. The girl shouts "what are you doing up here", which in turn triggers the guys memory of what his grandmother told him of some urban legend of some sorts. The girl is actually pointing to the pipes, but the guy thinks she is pointing to him. (The pipes were being carried by the other person, but he dropped them). This freaks the guy out, though he tries to remain calm. He turns to go leave, but since he is so freaked out, he forgets how to actually open the door. The pipes that hit him, were dropped by some other person that was on the rooftop with the guy and girl, but the guy didn't notice the person. The pipes then proceed to hit him in the arms, legs and head, which of course, knocks the guy out. Seeing this, the girl and the other person on the rooftop check him out, and go through the door to go call an ambulance or something. While they are gone, they lock the door to make sure the guy remains up there, where they know he will be, just in case he has some brain trauma or damage from the pipes. He regains consciousness while the two people are getting help for him, which makes him assume that she was a witch because the door is the only way out from the rooftop, the door is locked after he regains consciousness, and he doesn't see the girl anywhere.

SO CLOSE!
There are only 2 people in the building before and after the guy became unconscious
Just a little bit of tweaking, you have gotten most of it!

Okay, 2nd try:

The guy goes up to the rooftop after he got done with P.E. He goes through the door to see the girl up there, and pipes coming at him. The girl shouts "what are you doing up here", which in turn triggers the guys memory of what his grandmother told him of some urban legend of some sorts. The girl is actually pointing to the pipes, but the guy thinks she is pointing to him. (The pipes were being stored above the door area, but were knocked down or out of place by some outside element [like wind or an animal]). This freaks the guy out, though he tries to remain calm. He turns to go leave, but since he is so freaked out, he forgets how to actually open the door. The pipes then proceed to hit him in the arms, legs and head, which of course, knocks the guy out. Seeing this, the girl checks him out, and goes through the door to go call an ambulance or something. While they are gone, she locks the door to make sure the guy remains up there, where she knows he will be, just in case he has some brain trauma or damage from the pipes. He regains consciousness while the girl is getting help for him, which makes him assume that she was a witch because the door is the only way out from the rooftop, the door is locked after he regains consciousness, and he doesn't see the girl anywhere.

Yep, there's no contradiction. either way, the number of people still stays the same.

Did I get it right? My second narration?

YEAH! That's one of the possible solutions!
We have a winner!

Shall I write my solution? and I'll proceed to the continuation.

Okay. I wanna see how close I got. :3

Er, how were the pipes floating in mid-air? Or was that just the protagonist's messed up sight? But still, what kind of position were they in for him to see them like they were floating in the air? Also, what was the girl doing?

The guy came through the door at the wrong time. And it was also his messed up sight. Also, the girl was part of the maintenance staff. Hence why she sounded angry when the guy got up there unexpectedly.

The guy goes up to the rooftop after his PE class, he heard the girl's anguish. which means the girl is hit by those pipes. The main character still goes on through to check who is that. as soon as he enters the rooftop : he was amazed on how the pipes are flying into the air(resulted by a magnetic experiment). As soon as the girl notices him, points her finger to watch out from those flying/falling pipes. unable to escape due to panic - The pipes hit the guy and made him unconscious. The girl, seeing that the guy fell unconscious by those pipes - promptly went out of the rooftop, also the whole building to seek some help.

One of the maintenace staff goes inside the building and locks every staircase. By starting from the top. As usual - that man locked the rooftop. and proceeds on locking every staircase. and leaves the building.

The guy who was locked inside, wakes up and does his thing. and tries to wreck the door, unfortunately - the door is sturdy

As soon as the girl had asked for help, founds out that the 1st floor staircase was locked, telling one of the maintenance the whole story and proceeds on saving that guy.

Mystery Solved!

Reconstrucing another one..

So apparently, there were pipes on the top of the little room that leads out to the rooftop that fell on him? And he was able to look at the pipes falling on top of him and the girl in front of him both at the same time to even create the faint illusion that she was levitating them "around her"?

How about if...that's a science experiment? or a construction site?

Then we'd have to question what kind of science experiment could that possibly have been? And a construction site? Well, alright, but then who would store pipes there?

Magnetic levitation, it works by using electromagnets.

and that rooftop isn't small like the one I posted. I forgot to draw the whole building structre.

Electromagnetics? That could work. Who would store pipes on top of anything, where they could potentially fall, as they in fact did? Wouldn't it be easier to lay them down somewhere?