Some years ago I bought a cashmere dress that I really liked. I wore it endlessly, to the point where I had mended it way beyond what was reasonable. I would have liked to buy another, but unfortunately the company that made it had altered the style soon after I bought mine and the new version had features I disliked.
So eventually I decided the only solution was to make my own similar dress. And I'm wearing it as I type this.
It is not at all difficult to do if you already have a garment you can measure as a basis.
I wanted a long-sleeved dress (the original had had three-quarter length sleeves), I wanted it a bit below knee length (longer than the original), and I wanted it to be raglan instead of with set-in sleeves.
I started with a large swatch on 2mm needles in a black 100% cashmere yarn. As my yarn was an oiled industrial yarn I washed and deoiled my swatch before measuring it.
Then it was a matter of drawing an extremely basic sketch of what I wanted and putting in measurements. As I was going to knit seamlessly in the round I started with circumference measurements (of the existing garment, not of me!) I adjusted these measurements to add length to the skirt and sleeves.
Then I could convert these measurements into stitch numbers on the basis of my swatch. The lengths between the points with different numbers of stitches gives you the number of rows, making it easy to see how often to decrease or increase to get the right numbers.
As this dress was stocking stitch with turned up hems, I did not have to consider ribbing, and I knew that my basic raglan decrease could happen every other round.
I'm about to start knitting another dress to this pattern, and the only change I am going to make is to start the front of the neck a centimetre lower and raise the back of the neck slightly.
As long as you have an existing garment which you like the fit of, it really is easy to create your own garment!