Smile at him every time you see him. Say hello. Go talk with him. See if you have anything in common ( hobbies or sports interests ) Ask him to lunch. If you do this, he will start to get the idea you are interested without it being too obvious.
Usually romances between Co-workers end in a fiery disaster, so be careful if you do date. Keep work and dating separate. Just try to strike up a conversation with him. Talking to him will help him notice you.
