YA fiction: main characters hide out in roof of school library

[Peter]

This book was on required reading list in high school, but all I can remember is the main character(s) hid out/lived in the roof of a library, I think the school library.
That is all I can remember about it, but its been driving me crazy for weeks.
I was in high school in the 90's, so would be popular back then.

[[deleted user]]

In The Neverending Story Bastian hides in his school’s attic.

[Peter]

Love that movie/book, but nah thats not it.

[Daisy]

Not YA, but Help! I'm a Prisoner in the Library!?

[Daisy]

Also, I think the main characters in The Girl Who Owned a City lived in a library and/or school for part of the time.

[Peter]

Its neither of those books either, thanks for trying though.

[Rainbowheart]

Were the characters in high school, or younger children?

How many do you think there were? Any idea if they were male or female?