Well mate, for a start, you need to make yourself known. Eye contact is a start but it wont get you the girl. Next time, grow some balls, make a passing comment e.g. "it is nice out there", "havent seen you around here before, where have you been hiding", "which department you working at", etc. etc and introduce yourself and start a conversation but dont be creepy. Your body language is important. Show her you just one sociable guy who likes to get to know her. Send her an email if it is permissible at work. And with time, start building rapport and attraction. And eventually ask her out.
And yes, Im talking from experience