Mark the location for the roof vent by driving a nail through the roof sheathing. Center the nail between rafters 16" to 24" from the ridge pole.
Center a vent cover over the nail on the outside of the roof. Outline the base flange of the vent cover on the shingles, then remove shingles in an area 2" inside the outline. Mark the roof vent hole using the marker nail as a centerpoint. Cut the hole using a reciprocating saw or jigsaw.
Apply roof cement to the underside of the base flange. Set the vent cover in position, slipping the flange under the shingles, centered over the vent-hole cutout.
Secure the roof vent to the sheathing with rubber gasket nails on all sides of the flange. Tack down any loose shingles. Do not nail through the flange when attaching shingles.