Here's a video on how I made a digitally designed shirt with fabric printing.
I used Marvelous Designer for the 3D CAD file and the fabric pattern. The custom avatar was created based on my measurements using Make Human. I used Blender to apply the graphic prints, using UV textures. I printed the fabric through Spoonflower. And the t-shirt was cut and sewn by me.
This method gives me a custom fitted shirt with custom graphics. As a novice pattern maker, I can digitally preview how my patterns are sewn and make adjustments without wasting time and money on samples. As an end user of the product, I get a shirt that actually fits my body and my style preferences.