last link in my sig. Thats the best tutorial on scaling pepakura armour out there that I know of. It it can't help you, then PM me after you nhave tried it more then 3 times without success. Make sure you try all 3 methods!
All you have to do is insert numbers in the red boxes and Tada, you end up with the proper Pep Scaling Numbers to achieve a perfect fit for any height.
It's not perfect, you still have to measure an image or a model like Method #1 states, However,you could use the image Xtreme provides in his tutorial to measure out.
When I do my scaling, I first measure myself for the armor piece that I am doing. Usually for the helmet, I add an extra 2 inches to leave room for padding and stuff.
Once I have all my measurements in inches, I convert it to mm since pepakura v3 works in mm. Since I usually measure for height, I just make sure I put my measurement conversion in the height box in pepakura when I scale my stuff. I have not had really any problems doing it that way.