How do I get the girl?

Yesterday I saw a really hot girl at work. I work at a school and there is another building next door on the school compound where I saw her. I think she is a secretary or something. I saw her walking into the building but I pretended I wasn’t interested or attracted to her. I just greeted her good morning and she replied as she disappeared into the building. Now I know what most of you will say…just go in and ask her out. Keep in mind, she does not know me, she knows she is hot and probably has a lot of guys hitting on her. What do I do to get a date? How exactly do I get to know her?