There are so many different things you can do with pre-existing patterns to get what you want in a costume. This tutorial just lists a few examples, but hopefully it's something that can get you started if you've never tried this before!
Some experience with patterns might be required to understand this to the fullest.
Also, please excuse my typos. XD I made this late at night haha.
Attack on Titan/Shingeki no Kyojin is (c) Hajime Isayama