There's a lot of chat and only one picture of a ptiched not flat roof but will give some idea.
diy-extra.co.uk. or pop in to your local library and look up the DIY books. or email me I have sent someone on this forum a couple of weeks ago instructions which I still have you have to sunday to request them after that I'll be away working. robertwhiting76athotmail.com change the at to normal email symbol
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix roofing.