I WISH I'D had this book five years ago when I tried to "design" a sweater (never finished). I would have known how to adjust for various yarn weights, could have more accurately measured the amounts needed and figured out a better color scheme.
This treasure of a book doesn't just show how to knit a basic cardigan, for instance; it shows 16 possible cardigan variations with individual instructions (brief, to be sure, but easily followed); nine variations for a square neckline; five hood versions and so on.
The authors (both live in Seattle) give detailed guidance in making your own design charts, including picture knitting (transferring a graphic design into a knitting pattern); in fact, there is just about everything a knitter needs for positive inspiration. I have ripped out that old sweater and am now embarked on a new design--one that may have a chance of getting finished. ($29.95)