The main thing is to communicate with him! He might be thinking of asking you out too but maybe is shy or wants to find out if you like him first.
Just start talking. A simple 'hi' with a smile when you see him in the hallway to break some ice...talk some bullshit for a bit, hell talk about minecraft, (if he's into that sort of thing)...then just drop a bomb like 'so you wanna go out sometime' or 'we should go to see 'blah blah' if some movie come out and you both not seen yet... and say it with so much confidence like you know he's gonna say yes before he even says it. See what happens!
It really depends on a lot of things but If you sit around waiting for one guy to ask you out all year then you are gonna have a crappy year, it is better to just ask him out and if he says no you can move on and if he says yes then you can start a relationship or whatever.
Ask on a friday for the weekend or for next friday,that way if he says no then you don't have to see him again until monday and you can have a great weekend, or at least come back on monday giving off the impression that you had a great weekend. *wink wink*