The 20-year-old Academy product will stay with the Robins until January 4 having spent a loan spell with Northampton last season.
"We have seen Kemar a number of times over the past few years," Yates told the club's official website.
"He is a wide player who can play up front but he is predominantly a left-sided player who can use both feet. He's an exciting player and we have done well to bring him here on loan."
Roofe follows Toby Ajala and Connor Goldson into the squad for Saturday's trip to Southend.
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