Have a hip roofed duplex with shared attic. There are no gable end walls to mount louvres. I would like to mount a ceiling whole house exhaust fan and duct directly to roof. Problem is finding a roof louvre large enough to exhaust 4000 cfm to 6000 cfm. Graingers on-line seems to want to direct me to roof louvres that have an exhaust fan already mounted in the roof louvre. My roof is 9/12. Where can I get a louvre large enough? I can build curb if need be.