On a former factory site at Narrow Lane in Llandudno Junction, the proposed office building will have about 8,600 sq m of space.
The authority is seeking a contractor to finalise the design and build the complex, to house up to 650 staff.
It is expected to feature open-plan working spaces and meet the "excellent" standard under the BREEAM environmental rating system.
The value of the contract is expected to range from £18 million to £22 million, with the project due by summer in 2010.
Up to five bidders will be invited to submit formal tenders. The deadline for requests to participate is Friday 25 April.