When you say you have to make a flight plan can you be a bit more specific. Are you expected to produce a manual flight plan? This requires actually routes from the airport, using a departure and airways, across the Atlantic maybe a NAT track (daily specified track) and then airways in USA to an arrival into Chicago O'hare. Are you expected to take into account winds? Nowadays this is done by computerised flight planning systems using actual aircraft, actual weights, the weather and the routeings on the day. If you start buying charts you are going to spend a lot of money. In aviation these are charts not maps! It gets a bit more complex as you are using a 777, which is a twin, so requires ETOPS planning using certain enroute alternates depending on what rule distance you have been granted. Sorry to say this is a complex subject for a student. But then again it depends what you have been studying as presumably your teacher is setting a question that you are equipped to answer.