With a Character Design Portfolio you want to include "Character Turnarounds" of as many characters in your personal story that you can. If you have multiple stories with many characters of all shapes and sizes separate them per project. As you can see below the first project is "Sample Project 1". I duplicated the character sheet for "Char. One" but when you create your character design portfolio make sure to have at least 5-7 original characters set up in this manner. Try to play with shape form and have them look as diverse as possible so not all character look the same, unless you're going for something specific.