Queensland's auditor-general has questioned whether the state government got value for money from its CBD revamp.

No business case was developed for the William Street tower, a government agency hub to be built by the private sector opposite Parliament House.

An artist's impression of the proposed 45-storey tower to be built at 1 William Street. Credit:Woods Bagots Architects

Auditor-General Andrew Greaves says government policy wasn't followed and alternatives weren't investigated such as direct public sector ownership or leasing at other locations.

"While the costs associated with 1 William Street may represent value for money, it was not determined before the decision was taken, or subsequently, that it epitomises value for the state," the report said.