Slide the top and sides of your vent underneath the surrounding shingles and leave the bottom side of the vent exposed and laying over the shingles.
How to install a kitchen exhaust roof vent.
Nail the lower corners with roofing nails and tar the heads.
Route the vent hose tubing through the holes in cabinet and ceiling and push up into the ceiling.
Drop a plumb bob down from the roof to the wire so you can find the approximate roof exit location.
Connect vent hose to exhaust outlet and push excess into ceiling.
Next hammer in a nail every few inches to secure the vent to your roofing structure.
Some will mount from above while some will mount from underneath.
Insert the fan assembly into the opening you made in the cabinet for it.
Apply a bead of asphalt roof cement on the bottom of the vent.
The lower half of the flange sits on top of the shingles.
Back in the kitchen mark the cabinets and cut holes for the ducts.
Turn your vent upside down and apply a thick bead of caulk to the flange.
You may have to shift the vent position several inches to avoid ceiling and roof framing.