In the picture below you can see the pieces of a rod laid out before gluing. Depending on the action a person wants or what I want, determines where and how I do the hollowing. Some builders have systematic forms of hollowing (a 1" dam every 1/2"). I like to change it up in order to bring the rod to life. All of the rods I have made with the exception of one have been hollow built. I keep my wall thicknesses right around .040" thick. This rod is a 7'11" 4 weight that will be slightly medium fast. I want the flex point to be right about 2-4" above the ferrules, a powerful loading rod, but with a delicate tip for quiet presentations.