Due to a question recently asked on a sewing group, I thought I'd use my response to how to enlarge a pattern to the next size when the pattern is at it's largest of the typical 3 cutting/sizing options. I hope this will help or at least give some ideas of how you can go about doing this w/o buying a new pattern (providing you have some sewing experience;).
It really will depend on your sewing ability, the pattern, and way your body is shaped compared to the pattern. Usually you can increase w/no problem on the pattern where there are lines for doing so.
I would suggest getting the pattern out and spreading it out like a puzzle so you are aligning the pieces as if they were sewn together. Then measure your body and the pattern to see where you'll need to increase the dimensions of the pattern. Stick-it notes are helpful as you can jot your measurement and the pattern's on them so you don't lose track when it gets more complicated.
Then after all that, find garments that fit you well and spread them out with buttons and all closed, etc as if it was being worn. Then lay the pattern back out again on top of it. Then with the stick it's and pins (if needed), check out the areas you most need to custom fit such as chest, arms, shoulders, length, etc. Also compare the shoulder where your b straps sit and down to the center of the armpit area.
By this time you should know if you can use the pattern or if you need to buy one that is larger (smaller, etc.)
If needed, based on your confidence and ability, you can also trace your clothes you are testing against the pattern and have an idea there by laying the pattern pieces out on that paper tracing. IF it would help you even more, you can cut your drawn items into pattern pieces so you can work with smaller pieces for enlarging (or diminishing) the pieces.
Just keep in mind that your pattern is showing seam allowances and your clothing isn't so you'll have that difference to account for. :)
When I'm cutting out a new pattern, I cut it with all the sizes and darts and such all left intact. Then I can use my tracing wheel or marking pencil to mark the material for the size I will be cutting it into. Sometimes I will cut some spots around the arms, crotch, neck area so I can fold the pattern seams for the larger sizes and not cut them off. You can fold and iron them to make cutting much easier. When you first start cutting the pattern out, look at it closely and you'll learn a lot about how you can customize it to your own measurements.
I hope this helps!
I don't know about the rest of you, but I'm still having trouble blogging on this new format. I keep getting timed-out messages and my posts disappear before I can finish them. I've got a pink warning line message now. It also wouldn't let me upload a graphic/pic. This is getting really frustrating.