How do I make some custom sewing patterns for shirts/pants?
You need to learn how to draft your own pattern. This takes an good education and practice. Learning form a class or a person who is proficient in drafting patterns. Your public library would have books on this subject too. Google How to draft a pattern with measurements
It can be done, but pattern drafting is generally a college level course, and the textbooks are priced accordingly.Here's a starter for you: https://www.sewinganddesignschool.com/module/class.htm?classId=133102 Other resources include books on flat pattern drafting by Helen Joseph Armstrong. You may be able to borrow the book from your library, or the library may be able to get it on an inter-library loan. If you want to buy if for your self, buy one of the earlier editions: drafting doesn't change that much. You will be asked to do some math, and some understanding of geometry is useful.
Just search online. Or use a standard one that you modify based on your measurements
Go to YouTube and search.