I'm not sure exactly what you are saying. When the roof is installed, it is in one sheet and the holes for the vents, skylights, AC, etc. are cut out. The usual method is to cut diagonally across the opening from corner to corner - a big X. The sides are then folded into the opening and usually stapled or glued to the framing around the hole. The V shaped ends, if they extend below the ceiling are cut off just a little above the ceiling. The flanges of vents, skylights, etc. cover these pieces. Since they are usually hidden by the flange, how would cutting them create more light?
Maybe I am not understanding your question, but this is how the roof should be.
If you can clarify, maybe we can help.
Dave
Dave and Anna McCoy
:B :W
2012 Coachman Concord 301SS
2013 GMC Terrain Denali