The Auditor General Lynn Provost has criticised aspects of the Auckland Council's $200 million role in helping to develop a major new commercial centre in the north-west.
Ms Provost said cost-sharing arrangements between the council and a commercial developer for the Westgate development were complex.
She says it's not yet clear what the final bill will be, or whether the council will get what it expected.
The inquiry began after complaints from several Auckland councillors about the development, which was driven by the former Waitakere City Council in 1999.
Ms Provost said some cost sharing agreements made by Waitakere were not passed on to the newly formed Auckland Council in 2010, and some had to be renegotiated.
She said the council's risk had risen due to payments from the developer being allowed to be deferred, and the council should take a greater role in overseeing the ongoing development.
She also said the council should have been more open and transparent about the arrangements, and that an internal legal review conducted by the council should be made public.
The council has welcomed the report's recommendations and has made public a redacted version.