Why would I want to make my own blocks?

So you can make your own patterns using these blocks.  Which leads to the next question:  Why would I want to make my own patterns?  For one or more of the following reasons, though there is quite a bit of overlap with some of them:

1. Commercial patterns don't fit well because your figure is different to the Standard Figure in various ways.  You have to make lots of adjustments to make them fit better, or you don't know how to make adjustments to make them fit better.
2. You just want to learn the basic concepts to help you make changes to Commercial Patterns.
3. You don't want to be limited to the styles in the commercial patterns, you want to make your own.
4. You find it hard to find exactly what you want in patterns; you might like a general style but making certain changes would make it a better style for you.
5. You want to express your individuality; you want to make some crazy-ass type styles that look like things that top designers make.
6. You want to study patternmaking but can't afford to do an accredited course; you'd like to learn the basics in the meantime.

Commercial Patterns don't fit well because your figure is different to the Standard Figure in various ways

It is possible to make adjustments to Commercial Patterns to make them fit your figure, but the more you differ from the standard figure and the degree to which your body differes, the more time difficult and time-consuming this is. If you have made your own block, which is made to your measurements, then (assuming you have made toiles and tested that the measurements are correct), it means that the patterns that you make result in better fitting garments, and you don't have to much fitting work when you make the garment.  It means that you don't have to make alternations various pattern pieces. 

[After reading this article, come back and click on this link:  Where do I start? How do I learn patternmaking? Once you learn the Principles of Patternmaking and make your own set of Blocks, you will not be limited to the styles in commercial pattern libraries.  Eventually, you can make any design you want.  You may have a dress that you purchased that you love the style of and you want to be able to make another: you can just look at the design lines and recreate that dress.  You may watch a 1940s movie and love the dress the heroine is wearing; you can look a the design lines and recreate it for yourself.  Of course, it will take some time studying to get to that, but after you learn a certain amount you then just add a bit here and there as you need it. The more common course of action is, of course,  to buy Commercial Patterns,  which in a lot of cases won't fit well and will need some kind of adjustment. How many adjustments you need to make will depend on how much you differ from "The Standard", and may take a fair amount of work.  Your shoulders may slope more or less than the pattern, you may have a larger bust size, you may have a sway back, forward-sloping shoulders, large shoulders, narrow shoulders, square shoulders, prominent shoulder blades, full upper back, rounded back, large neck, hollow chest.. or any other number of figure "issues". They are issues (and not a "figure fault") because they haven't been accounted for in the pattern, and you will need to make adjustments to the pattern to make it fit well. Some of the commercial patterns nowadays suggest that you tack or baste the dress first, then mark where you need to make adjustments, then unpick and re-sew making the necessary adjustments.  This takes quite a bit of time. On top of that, there are some things which can't be adjusted at this stage. If you are new to sewing there may be a number of problems and you don't know where to start first. 

It Does Take Time

Yes, it takes quite a bit of time to learn to make your own patterns, but if you are serious about wanting to make your own clothes, and especially if your figure is different to "the norm" in a number of ways, then learning to make your own patterns is the smart and sensible way to go.  The time put into learning will be well worth the effort. To learn patternmaking you don't have to make everything full scale.  Learn by practicing using Third Scale Blocks (which you can download if you click on the link), and you can follow along with the instructions for any of the Patterns.  The instructions are step-by-step and refer you to the Principles.  You can make practice patterns with Third Scale Blocks until you are confident with the theory, then make your own Block and make your own patterns.