Well, this kind of thing can certainly be accomplished. As for how difficult it is, that will depend on your knitting skills, ability to visualize things in 3-D, and math skills (you’ll have to apply a yarn/gauge to your creation).
If you have some pictures of what you want to make, I suggest looking for some patterns with similair shape/style. Read them over really well and become familiar with the techniques used (bottom-up, top-down, pattern, edges etc). Then either start adapting those patterns, or applying the techniques to your own pattern, to make the cardigan you desire.
Once you get something started, pattern-wise, you could certainly head to your LYS for some help in tweaking things from either the shop staff or other knitters who are just there browsing.
I just saw a sweater pattern generator. You put in the type of sweater you want, the yarn weight you want to use, and the size and it automatically gives you a pattern. It’s at the top of this web page. http://www.knittingfool.com/pages/sweater_wheel.guest.cfm