The Millers are back in the second tier after a glorious League One promotion this year and they will be aiming to avoid a fourth successive relegation from that division.
Warne is planning an overhaul of his squad as he expects to lose some key players, with Michael Smith and Michael Ihiekwe out of contract and Chiedozie Ogbene and Ben Wiles set to attract interest from other clubs.
Several other players, including record signing Freddie Ladapo, could leave, meaning Warne will have to be active in the transfer market.
"Are we going to lose a couple of players? Maybe," Warne said. "Will we have to recruit other ones? Yeah.
"It is a very, very difficult ask but we need to recruit seven, eight, nine players who are better than the ones we have.
"Nearly every year I've been a manager we've had to rebuild the team in the summer. This year is no different."
The Millers are in a strong negotiating position if any clubs come in for players still under contract and Warne insists the club will not be strong-armed into selling.
"Unless the money is right they won't be sold," he added.
Warne is also keen to bring his three loan players back next season.
Will Grigg is out of contract at Sunderland and likely to be offered a deal by Warne while Rarmani Edmonds-Green and Jordi Osei-Tutu will return to Huddersfield and Arsenal respectively.
“I liked all my loan signings. I loved Griggy, Jordi and ‘REG’. He got (briefly) injured and we only got Jordi match-fit right at the end and Griggy was flying until he got injured.
“I would like to keep all three if I possibly could or consider it. In fairness to Jordi, he is an Arsenal player and it is about what they want to do, not what I want to.”
All three players are part of the Millers squad that is jetting out to Las Vegas this weekend to celebrate their promotion.