So you might be wondering right now, what gives, Melissa? I mean, didn’t we start with the skirt block because we know it fits?!?
And that’s a really good accusation I’ve just imagined you making. Here’s the sitch:
A skirt block doesn’t follow every single curve of your nether bits. (If you’re under 25, reading this, and wondering what I’m talking about because your clothes are all shrink-wrapped to your body, I’m sorry – we’re talking about different fabrics. I’m talking about honest, woven, non-spandex-y goods. They might come back into fashion again some day.)
A non-stretch skirt block actually can’t follow every curve of a curvy body, because it’s not nailed down to anything after the waist. So if you give it the length to follow a curve at the small of the back (like, if you’ve got a well-defined bubble butt), it will look a mess – use a heavy fabric, and the curve will stand out rather than following the body. It’s all bad.
As soon as you nail things down below the waist (with your crotch), it gets harder to skim over these curves. As the amount of junk in your trunk increases, the differential between a skirt block and a pant block increases. There’s fanciness you can do with slash and spread patterning to get the increase in exactly the right place, but this will get you started.
Once you’ve got your block fitted, transfer the changes back to the original draft. I’d recommend putting the resulting block on something that will withstand some wear and tear, unless you’re only going to use it once.