When I first started looking at estimating sheets I wondered why bath fans were so expensive. I understand now not rocket science but you can really mess up someones siding or roof if you dont know what you are doing. Some of the higher end fans have 6" duct.
Some insurance underwriters exclude roof cuts from ther coverages, and I bet a lot of guys have no idea the liability they take on when they do anything that can cause water entry, a CE course we took on insurance coverages, one of the presenters said water damage is something that never goes away, once the mold comes the party is over, may not be rocket science, but as many said, if you don't know how to close the opening, don't do the job, either way price it for profit, excluding it from the bid, will only cause conflict with the GC later, Try to list and price the tasks, wire and mount fan xx$ install vent duct xx$ roof cut xx$ then total it, call attention to the items, so the GC understands the scope, and is aware of your efforts not to, try and sting him for an extra later.
