Yup, I agree with OM. Your "sleeping height" is taller than your "standing height" because your toes extend when you sleep. A quality bag manufacturer will take this into account and size there bags according to your standing height. If you plan on making the bag yourself then your going to need to make it longer than your "standing height".

You don't want dead space at the end of you bag because then your toes will have to heat up that air. Get the bag to fit your needs.