I had someone replace the felt on my shed roof only two years ago and it couldn't have been done properly as it is now leaking at the joins very badly and the wood on the roof under the felt is soaked. I am thinking of redoing the roof with bitumen corrugated sheets so they may last longer than felt. I am going to do it myself but has anyone used this before and any tips please? The shed is about 8 x 10, stand alone, do I need to remove the felt beforehand or can I just put the corrugated sheets over the felt to save some work/time? Thank you for any assistance anyone can give.