I personally haven't created any pants or shorts from patterns for this exact reason. However since deconstructing several pairs of blue jeans I am noticing each pair have looked entirely different.
The only advise I can give to you is to take an old pair of pants, that can no longer be worn due to holes or fading, and deconstruct those to make your own pattern. From that pattern you should play around with rise and fit, to make an AWESOME pair of fitting pants/shorts.
I personally hope to try this out soon for myself, as I have found the perfect pair of blue jeans that fit me, and want to make them in other colors (NOT bleaching them and dying them into different colors, since bleach is not friendly, in any way).
I really hope this helps you, and feel free to contact me if you do go this route, or have other questions. (I am personally more of a dress/leggings person, but I would love to try to help!)