What should I do about this !?

So at work there is this guy and we keep looking at each other but he works in a different department then I so I don't get to talk to him that much which really sucks. But we keep looking at each other and saying hi or what's up to each other when we pass by one another. Now I think he's gay but I'm not sure. But I really want to start texting him to start to get an idea of what he likes but I don't know how to ask him for his number in a way that wouldn't seem creepy. Can someone please help... I suck at this shit haha