Ken:
It is a raised section in the middle of the ridge area.
If you do a Goggle search for "barn monitor roof", and click on images you'll see lots of photos of barns with monitor roofs.
Some go gable end to gable end, some don't go all the way to the ends.
These are usually used on small shed, or shacks where they boil maple sap to make maple syrup so that the steam from the boiling of the sap can vent out the top of the building through the roof.
If you Goggle search "sugar house" and click on images you'll see some with the steam pouring out the roof vents....
Hope that helps.
Jim
