On the Qantas website when doing an award booking use the multi city destination feature and put in the city pairs for multiple sectors. The award booking engine will calculate the required number of points as you start selecting flights. There are some rules like you must include 2 carriers other than QF on the itinerary, must keep it down below 35,000 miles, limited to 16 sectors, 5 stopover cities, no more than 2 stopovers in the same city etc.
If you can't book online then you can certainly use the QF service centre and they may charge you an extra 2,500 points. Total cost 142,500 QFF points for a Oneworld RTW award. In my opinion it is the best value for QFF points or even Amex MR points.
There are a some threads on AFF with more detail if you are interested in the booking process.