Creating our film's plot

As of yet we have not yet found a definitive plot for out film , but we have some key ideas that we can use to advance our ideas.
Our production will be mainly filmed in school, which won't be hard to create an eerie environment.
I like the idea of the film "triangle" where the audience pick up clues along the way as to what is going on and go as far as to question was the whole film the main characters dream.
With this idea I can create a sort of brief outline of a plot.
A boy who goes into school one day to find no-one there (is he dreaming? is this real? or is this a set-up?) and he wanders around the school, cautious as to whats happening, and it is apparent that he is being watched.
This is only a very brief mock-up , but as the group discus we will advance on this.