If you have the vibe of a social guy this should be easy.. You can start by saying hello to everyone once you walk into the elevator.. I do this all the time, as a matter of fact, I say hello to everyone pretty much every where I go..

For example walk into the elevator and say " Good morning guys" and then make a simple joke like " so who's taking me out for coffee" This sets the stage for you sparking different conversation the next time you see them around the building or in the elevator again.

If you experienced just walk in the elevator and open one.. " Hey cutie, im going to need your number before this hits the 6th floor" and then hand her your phone.