You should visit the Model Overview page if you don't already know what model you want, and the Materials/Color Zones page to see all the options (except suede colors). There are lots of Extra options too.
There are a few models that can't be ordered from this page, just because they're a bit different. And you will need to list your color/material choices per zone in the Text box at the bottom or else we will assume you just want black oiled nubuck.
If you've never ridden in a Ghost saddle before, please consider doing a demo first. This may not be necessary for the BBP and Flexx option unless you aren't sure how the thigh blocks will work for your riding position.