The Encyclopedia of Knitting by Lesley Stanfield and Melody Griffiths has a section on designing and charting, and it is specifically for a sweater. I've used the book often for stitch patterns and general help, but I'm not to the point of designing yet, so I don't know if the chapter is any help or not.
See if you can check it out from the library, that's how I always get my books, and see if it's worth it before you buy it.
You HAVE to post a pic once you get your sweater under way!!!