Sewing patterns; are you able to draw your own or need to buy them?

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I've been learning how to sew from my mother who has done this for years. She basicly knows how to draw very simple patterns, but mostly she will use existing ones and change them to what she wants to create; drawing a full pattern is hard for her but she knows how to make changes to patterns. Because my mom doesn't know how to draw these patterns, I also haven't learned so far. This is why I buy a lot of patterns and change these existing patterns. I would love to learn how to draw patterns eventually. Are you able to draw your own? Do you like it, or does it involve a lot of time and effort? Do you like the patterns available out there?