If you're talking stepped flashing like you see on chimney stacks and parapet walls between houses on roofs then send email to robertwhiting76@hotmail.com and I'll send attachment pictures from my building book. Send picture of where the flashing has to go. It's an apron not flashing will explain if you e-mail.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix roofing.