Hermione was on the roof. Alone. This time.
Actually…
She was up there, hiding, but she didn’t do a good job. Everyone else was sleeping. So she didn’t hide from anyone of everyone. She just hid. Or something…
She looked at the stars, on the sky, in the night.
That always made her horny. The stars… Strangely enough. Or it was the cold that made her nipples stand out. We don’t know. 
Her nipples stood out, through her shirt. Pointing, or something like that…
Maybe this only was a cheap attempt to make her nipples point out. In fact, no one knows if they did, but Hermione. And she never told.
Anyhow, she was on the roof. I told you that already, haven’t I? She looked at the stars, and masturbated. The masturbating part is about as unsure as the nipples pointing, but it is now a common belief. The rumors’ go that Hermione masturbates on the roof, so therefore, she masturbated on the roof. No point in rumors if you don’t believe in them… 
So, for the point of porn, she masturbated on the roof. You just have to believe me on this one. She sat naked, under the stars, touching herself sneusally. She probably moaned as she went on. She came, in a wonderful and sparkling orchestra of colors. She came hard. Trust me.
Then she went down, from the roof. 
After that, the roof was empty.
This is fun.