The 22-year-old, who worked with U’s head coach Michael Appleton at The Hawthorns, grabbed six goals in the last seven games of the season.
That form led to him being nominated for the Sky Bet League Two Player of the Month award and also saw him attract interest from other clubs.
But after committing to Oxford by signing a three-year deal, Roofe told the club’s official website: “It was an easy decision.
“Not only have I enjoyed my football at Oxford and been made to feel really welcome but I have also seen how ambitious the club are.
“We finished last season really strongly, the bulk of that side will be here next season and there is a really positive atmosphere around the whole club.
“The fans played a big part as well. They have been great with me and I would love to be part of a team that brings them the success they deserve.”
Appleton said: “He did really well last season. He is quick, he has an eye for goal and he does things defenders aren’t expecting, which is always going to make him dangerous.
“He got better with every game and I honestly believe there is more to come from him so it is an excellent signing for the club.”