I used pre-insulated flex ducting, which is good for this sort of vent (not good for a kitchen vent...) and just moved those over once the proper vents were installed. I decided to go straight up through the roof to keep the vent runs really short to minimize the chance for condensation. The gable would have been ok, but the nearest gable faced the street, so it would have been a bit ugly. If it was facing the side of the house, that would have been easier/cheaper and I would have done that. The original builder had left all three bathroom vents open into the attic ( grumble !%$?!) so I had them all fixed at once. It was a bit of a challenge to find a roofer to even show up for such a little job. In the end, I overpaid a guy $500 to install three vents into the roof (asphalt shingle). I had to go into the attic and attach my flex ducting to the inside of the new vents.