Waar wrote...
alright so I work as a barista at starbucks and I have to tell you, flirting is awesome; if you can sneak in some comments about how you're single or something he might get the idea but i would avoid doing to "approach him after work" idea; inquiring about his shifts may also seem stalkerish. If you really wanted to take a shot you could simply leave him your number, if he calls you win and if he doesn't no problem, it never happened.
Dammit, stole the words right from my mouth.
You could also try casually sneaking questions to him while conversing like,"you married?", or "You know, I've been here quite frequently and seen you around a lot, but I've never caught your name", which is essentially flirting, but hey, it's just an example on how to go about it.
Seeing as he knows your face, leaving your number is actually a very good idea. The simple act of replying to you answers a number of questions, most importantly, that he's single. It also means he's interested in you, and that, at the moment, he has the free time to talk, the act also tells you that he will probably want to meet with you in person, at a time he is free, and hopefully you are too. The most important thing to this process is not only do you leave your number you must also leave a name so he can mentally connect your name with your face.
And the whole, wait after work thing, don't do it. It's cute in highschool, or if you're already dating the person, but when it comes to introducing each other, it does not bode well.