Hi there, I get foils so I understand roots, I go to a light brown/dark blonde from a dark brown. I typically can't go about more than 5 or 6 weeks because the roots will drive me crazy if I wait past then but I think that most stylists may say, get them touched up when you can't take the roots anymore, it's up to you. Some people don't mind having roots, I wish I was one of those - LOL!
Good luck!
Amy