In the 1960s the government proposed an extension of Parliament House, which had only been partly built in 1922. Prime Minister Keith Holyoake had wanted to complete the original plan, but the government architect persuaded him to approve a modern building which would house parliamentary offices. In 1964, Scottish architect Sir Basil Spence provided the original conceptual design of a round building rising in steps. The detailed architectural design was undertaken by the New Zealand government architect Fergus Sheppard, and structural design of the building was undertaken by the Ministry of Works. W. M. Angus constructed the first stage, beginning in 1969 – the podium, underground car park and basement for a national civil defence centre. Gibson O'Connor constructed the ten floors of the remainder of the building.