A lot of the places will make a sample or design the patterns based on your drawings, renderings or Illustrator files with basic dimensions.
As with everything, the more specific your drawings are the better. Side, front, back, bottom, top, 3/4, etc. If you just give them a couple of 3/4 views then they will use their best judgement and you will be at their mercy.
It’s usually a lengthy process going over several prototypes until you are satisfied with the way it looks and the pattern maker/manufacturer is happy with how it will go together.
For very complex shapes we would have a 3D physical model and she would wrap it with pieces of paper taped up together. Once the whole model was wrapped in paper she would draw the pattern pieces trying to avoid complex shapes/turns/bends etc. It’s an art form. After she had drawn the different pattern pieces she would go ahead and cut them leaving her with hopefully flat pieces that would then be traced and cleaned up onto cardboard for the final pattern pieces.
It’s usually a process of the designer working with the pattern maker and the person sewing. Hope this helps.