Thanks for your interesting question, Anu.
Parliament House has been designed to last 200 years so it should be quite a while before we need a new one!
Built into Capital Hill in Canberra, Parliament House was opened by Her Majesty, Queen Elizabeth II, on 9 May 1988. This followed an international design competition and 7 years of work to construct one of the largest buildings in the southern hemisphere.
Parliament House replaced the provisional parliament building (now known as Old Parliament House) which was only intended to be temporary but ended up being used for 61 years (1927-1988).
Despite its size (300 metres long x 300 metres wide) and having 4 500 rooms, there are already some days when Parliament House is filled to capacity. On busy sitting—meeting—days there are usually 4 000 to 5 000 people at work in the building.
If these numbers continue to grow, Parliament House—like Old Parliament House—may be unable to accommodate everyone.