South Yorkshire Police hopes to build the 50-cell suite in Shepcote Lane, near to Meadowhall shopping centre.
It will replace suites in Ecclesfield, Sheffield and Rotherham, saving more than £1m a year said the police.
Ch Supt Rob Odell said it was hoped the new suite would be completed by the summer of 2016.
He said: "We anticipate that replacing three existing properties within Rotherham and Sheffield with one purpose-built facility will deliver annual savings of approximately £1.2m.
"The majority of this will come from a reduction in staffing, but there will be other revenue savings and energy efficiencies too.
"We are consulting regularly with the staff affected, who are mainly custody sergeants and detention officers, and we hope to achieve the savings through natural wastage."
A public consultation on the plans has begun.

Friend, 28, was withdrawn during the 1-0 defeat by Nottingham Forest on 23 January after landing awkwardly.
Former Doncaster and Wolves full-back Friend has missed just one league game this season, scoring once.
Boro are already without centre-back Ben Gibson with a hip injury, who can also play wide, while full-back James Husband is on loan at Huddersfield.
Plans for a £19m police custody centre to replace three "outdated and inefficient" suites are being submitted to Sheffield City Council.
[NEXT_CONCEPT]
Middlesbrough defender George Friend will be out for approximately four weeks after fracturing a shoulder.