The report, which will be presented to councillors on Tuesday, outlines plans to further upgrade the city centre as the council progresses with the central city plan.
Councillors requested a report about various options for upgrading the Octagon in June.
The paper presented high level cost estimates for the Octagon, ranging from $15m at its lowest to $52m at its highest.
A business case for the remainder of the central city projects to completed during 2024/25 will include the Octagon.
The central city plan grew out of the need to renew the below-groundwater infrastructure and improve road safety access for pedestrians, cyclists, and motorists.
It is expected to cost about $78m allowing for construction-inflation on above ground work, with the bulk of this focused on George St ($31m) and Princes St between Rattray St and Moray Pl ($31.5m).
After the development of the business case, the earliest expected date for initiating construction in another quarter after works in George St and Bath St would be in the 2025/2026 financial year.