How to guage for velux windows. It's a bit of a controversial one this. I will not want to cut the tiles under a velux ever!! Not unless it's absolutely necessary to do so!! 9/10, you make it work by changing the guage as you go up the roof. Many people are saying just go up the dame guage and cut the tiles in to suit. !! But the kit does not sit correctly in the scenario, and you risk cracked tiles on the corner cuts Personally, I'll make them fit whatever. #velux #veluxwindows #roofing #howto