A book that I used since 1975,( and can still be found on Amazon.com) whilst running my costume/special needs clothing business that makes drafting patterns VERY easy is titled, " How to Make Your Own Sewing Patterns" by Donal H. Mc Cunn. 1st ed. 1975 by Galahad Books. The 2nd edition has a new chapter on how to make Your own mannikin to make Garb to fit Yourself. If You can draw straight lines using a yardstick and know how to draw right angles, then You can use this book!
I mean, Hey, if I could and can do pattern making using this book, ANYBODY who can read and write can do this. I'm sorry that it has take this long to pass this on to the members. I hope this helps as once One has the basic patterns parts, One can also find in this book how to modify said patterns.