I wish Cal Patch was older than me and wrote Design-It-Yourself Clothes about 15 or twenty years ago, because when I was 23 years old I would have stalked her. I think she's probably relieved this was not the case, but this is the book I went hunting for when we first moved to New York and I wanted to make my own patterns. Nothing like this was available back then, and if you've been wanting to design and sew your own clothing you're going to love it.
Since this book wasn't available back when I wanted it, I purchased a set of patternmaking textbooks at FIT instead and was immediately overwhelmed by them. Terms were used and not defined, previous experience (or classes) were assumed, etc. I quickly realized it would have taken at least two of me to get started: one to stand still and the other to take measurements and do fittings. It also would have required many hours of work just to get started. I didn't know where to begin.
Later I went to school for fashion design and it all became clear, but that didn't make the whole process any less complicated and time-consuming. I did eventually manage to develop my own set of slopers, but it shouldn't have taken more than a year of fashion education to develop the skills to make simple skirts and blouse patterns for myself. (Fortunately, the advanced education was been put to good use elsewhere....)
Anyway, I really like Cal's approach to making patterns. Instead of following the more traditional (and convoluted, although very technically worthwhile) route, she shows you how to draft a pattern using a set of measurements you take from your body. You'll still need to test the pattern (she explains how to make a muslin, or prototype, which is a simplified version of the garment used to adjust the fit before you cut your actual fabric and spend a lot of time sewing it), but with her method you've removed several steps and brought yourself that much closer to having a sewing pattern.
Having said all this, however, I need to add a few cautions before you run off to get the book and whip up a fall wardrobe for yourself. First of all, patternmaking takes time. Just drafting the pattern is rather time consuming, but it's the fitting and adjusting (and fitting and adjusting) and then determining how to assemble the pieces that really takes a while. So don't get the idea that you're going to stitch together a suitcase full of clothing for yourself before the holidays. Start with a simple project (the books start with knit tops, but I would suggest starting with a woven shirt since knits can be a little tricky to sew with good results) and take your time. Enjoy the process. From start to finish, drafting and finishing one garment might take you several weeks or more than a month. On the other hand, if you stick with it you'll have a pattern with which you're really happy and can sew again and again.
Additionally, in order to adjust your muslin and get a proper fit from your pattern you're going to need to learn how to make adjustments to the pattern. A number of good books have been written about this topic, and I would suggest that you purchase one or two because proper fit isn't always intuitive, especially if you're a little curvy. Either that or find a friend who has lots of experience with alterations and adjustments, because fitting something on your own body can be frustrating or impossible. (And boyfriends or husbands aren't always helpful or willing assistants. Trust me on this.)
You'll also need a solid grasp of garment construction in order to make good use of this book. The sewing instructions in the book are minimal (I'm sure space was a consideration here, plus the title says "Patternmaking" and not "Patternmaking and Sewing"), so once you've finished drafting and fitting and correcting your pattern you'll need to understand how to assemble the pieces. I would recommend that you practice by following a few sewing patterns to develop a solid understanding of construction techniques before you attempt this at home. (In other words, this is not something to attempt immediately after you've finished a beginning sewing class. Give yourself a little time to develop your skills before you attempt this book.) Once you have a good grasp of the steps you need to take and the ways to make a garment look finished, you'll have fun designing and making your own clothing.
(On a side note, I was amazed while reading this book to find how similarly we both feel about a large number of issues and areas. For example, I've never seen anyone else apply bias binding using the same method that Cal and I prefer. So I feel especially good recommending this book because we obviously think along the same lines in many areas.)