Thanks for your question Sam! The Australian flag and flagmast above Australian Parliament House was designed to be a prominent and recognisable symbol of the federal Parliament. The flag, measuring 12.8 metres by 6.4 metres, marks the exact centre of the building and was intended to be seen from most parts of Canberra. It is flown over Parliament House 24 hours a day, seven days a week and is floodlit at night. Parliament House is one of the largest buildings in the southern hemisphere. It is 300 metres long and 300 metres wide and has a floor area of more than 250 000 square metres. A big flag was needed to fly over such a big building!
To find out more about the flag, watch this video, Pinnacle of Parliament House, on the Australian Parliament House website.