Our builder used most of our three gables to create the attic vents. He covered the framing with a few layers of metal meshing which were then covered with cement clapboard (hardie siding). They simply spaced the bottom of each board 1/2 inch or so above the lower one. It looks great and should provide fantastic ventilation. We are in Southern Calif, this might be too much venting for a colder climate.

Go to the link below for details on how a 2ft gable vent and fan was put in. I am guessing your current gable vent is too small.

Here is a link that might be useful: How To Install A Gable Fan