The 23-year-old was a hit at Elland Road during the 2018/19 season, notching up 15 league goals.
And Itten bagged himself 20 goals for Swiss outfit St. Gallen last season.
Speaking about Roofe, Gerrard said: "Kemar is recognised throughout Europe as an intelligent attacker with an eye for goal. I look forward to working with him and recognise his potential to further progress our starting XI.
"He has experienced the pressure and expectation at Leeds United and has played on the continent which will stand him in good stead for his time at Ibrox."