Just got a job to start.The roof in question has been on around 5 years.250sq m.The so called roofer did not strip the roof and then nailed plywood sheets directly onto the existing(i kid you not).The existing being felt and woodwall slabs He then fitted a fibre glass roof on the boards.Needless to say all the boards have curled up fracturing the fibre glass.,needless to say their 30 year guarantee is not worth the paper its written on.Goood news is they will get a good job this time,bad news is if they had got me the first time(yes i priced it originaly) it would still have been good for another 20 years,no problem at all.