Are you asking how the vertical tail and rudder are designed on ASELs? I am not sure what the question is exactly. All the flight controls must be sized, selected for aerodynamic lift, given hinge moments, assigned deflection ranges, analyzed for aeroelastic response, set up for stress loads, and adjusted through many design cycles in an iterative process when there is a need for a fresh airplane. Then the controls must be tested either using approved expansion calculation codes or flight tested. If you want to explore aircraft design it is a fascinating topic that can absorb your mind for years. Raymer makes some decent aircraft design books, or you could probably get something simpler aimed at making model airplanes. My school used the popular ten volume series by Jan Roskam titled "Aircraft Design" which is probably overkill for most hobbyists.