The Glasgow giants won the Scottish Championship title this past season and will play in the Scottish Premiership during the 2016-17 campaign.
The Gers have already started preparing for life in the Scottish top flight, having made as many as four new signings.
Joey Barton has left Premier League-bound Burnley to move to Rangers on a free transfer, while Jordan Rossiter has departed Liverpool for the Gers.
Rangers had already agreed pre-contract agreements with Josh Windass and Matt Crooks.
Robertson has revealed how Rangers are planning to do their business in the summer transfer window.
“Our recruitment is very much done on a player-by-player basis,” Robertson told Sportinglife.com. "Mark (Warburton) comes to us and lays out the value he believes his targets will bring to the team.
"We don't have a budget as such. We wait for the players to be brought to us and assess whether we want to go for them and get a deal done."
Rangers will be aiming to win the Scottish Premiership title next season. It will not be easy for the Gers, as Celtic will have the strongest squad and will be favourites for the championship.
One should not be surprised if Rangers end up second or third in the league next season, but the fans will hope that the team at least give it a go.