He will be eligible for spring practice but must sit out next season because of the NCAA transfer rules. He will have three years of eligibility remaining when he returns in 2019.
The 5-foot-11, 215-pound Roof played in 11 games as a freshman in 2017, finishing with 17 tackles and two sacks.
Coach Tom Allen says he's eager to see what Roof can add to the Hoosiers. Roof helped Buford High School reach four straight Georgia state championship games, winning titles in 2013 and 2014.
His father, Ted, is North Carolina State's assistant head coach and defensive coordinator. Roof's twin brother, Mic, is a quarterback at Charlotte.