As one poster said, one option is to copy a piece of clothing you have. I was taught to lay out the clothing on a table on top of a large piece of paper. A newspaper can be the paper. Trace around it leaving a wider margin for any seams. Make sure to notice the parts or pieces involved in the clothing and trace each one. For example, a skirt may have a two piece back with a zipper in the middle and a waistband as well. Or a shirt may have a sleeve which is a separate piece so must be traced too. Notice the parts just as you would with a purchased pattern.This way you can reproduce anything you have. This is how folks lived in previous generations.
Another alternative if you have something which is wearing out is taking it apart and using the actual pieces as a pattern. Just use a seam ripper to carefully dismantle. And if only one part , for example the front of a skirt is stained, is beyond repair. One option is to cut out a piece of that portion and reassemble the clothing to continue to use it.
Another thing people do is to turn a collar after detaching and reattach so the top is inside. As the outside of the collar can sometimes be the only worn part of a shirt.