Inspect the roof to determine where the skylight will be installed and measure the size of the skylight. Go inside and find a location where each edge of the skylight will be bordered by roof rafter. Hammer a nail in each corner from the inside so they can be found on the roof. Mark a square with a chalk line on the roof to signify where the light will be installed.
Remove all shingles and underlayment with a shingle stripper. Cut out the opening with a circular saw. Cut carefully to make sure the proper cut has been made.
Cut a 2-by-4 to the size of the width of the opening and screw it into place across the top of the opening. Repeat the process for the bottom to allow the skylight a header to install onto.
Set the skylight into the opening and screw it in place into by screwing it to the header that was installed, inserting a screw every six inches around the entire perimeter.
Roll flashing around the perimeter of the skylight and nail it in place with roofing nails. Inspect the area to make sure everything has been properly sealed and no gaps or cracks are visible.