Some pattern suppliers have outlines for a range of sizes on the patterns you purchase. For example, the Green Pepper/Rainshed parka pattern can be used for every size from small to XL. This particular pattern is designed for a liner but can easily be made without. By modifying this pattern and using light fabric, I have made a pullover hooded wind shirt that weighs 2.7 oz.
I endorse OM's recommendation that you take a sewing course if possible. Sadly, I leaned how to sew by trial and error. I'm pretty good at sewing now but it would have saved me a lot of money were I to have learned to sew BEFORE I took scissors to pricey fabric. Doing a trial run with cheap stuff is also a good idea; I think I'll give it a try for my next project 😂.
May I walk in beauty.