Ideas for a Voldemort costume?

I'm going to a HP convention and dressing up as Voldemort and I'm not sure what to wear. I already have a graduation gown which I will wear over whatever I wear underneath but it's just sort of a robe, as in it doesn't tie together at the front. Do you have any ideas? :D I'm a girl by the way, might affect ideas as to what clothes I have lying around :)