Hi, I'm building my own extension and have made a bit of a cock up with the roof finishing height. It comes just under the cills for the 1st floor windows whuch causes me problems with the flashing. In my head I've got a few options, 1. Replace the cills with a thinner ones to allow more room or 2. Cut the existing cills to achieve the same outcome. There are 2 cills, each different sizes and there's about 50mm bewteen them and the roof. I know I should have got my heights right but it's my first try . Any ideas would be much aprreciated