The ex-Manchester United star said: "I got a call from my agent and I wanted to come, because it was a great opportunity for me.
"I didn't even have a discussion with my agent about money."
Meanwhile, Roma sporting director Gianluca Petrachi confirmed Mkhitaryan was "giving up a lot" to join the club - but is grateful he can help them in their youthful revolution.
Petrachi revealed: "The idea was to invest in important young people.
"In situations where we found ourselves at the end of the market, or we made investments in young people or operations like those for Mkhi.
"He is a top player with very high costs... the boy has given up on lots of money to come to Rome. Time will tell if we have the chance to keep players like that."