A Picture to a Cast On
For my first design, I thought I would start with an infant - 12/24 month size for ease of design and knitting samples.
I had a picture in my head of a simple cardigan, knit from the top down, with the button band worked as you go along and the sleeves knit after in the round.
I decided with a quick increase in the neck band to add a bit of a gather and for simplicity sake.
To figure out the cast on numbers, I did consult various patterns to give myself a starting point and also I looked at the final number of stitches including the sleeves in various top down patterns. Next, I calculated how to get from the cast on number to the final number and wrote down the various increase rows.
I knew I wanted to design a 0-6 months, 6 - 12 months, and 12 - 24 months size.
As I looked through patterns, it became clear that there isn't one size fits all - for example, the measurements in patterns for the 0 - 6 month size are not all the same. However, for reference I referred to the charts at the Yarn Council and added a little more give - meaning wanted the finished garment a little larger for a little more ease.
So my design process, at the present, is to write the pattern as I knit.
The picture above is my first sample - my first try at the 0 - 6 month size. I like the size and the basic shape. I changed the button hole placement in the actual pattern (less buttonholes and staring the first buttonhole sooner).
Please remember, how I am doing this, is not the "right" way - I am simply sharing my process.