I think some here are over-thinking this project. String together a bunch of strips. Cut the first strip whatever length you want---------40" is what you want. Keep adding strips until you reach 36" wide.
If you are using from your stash-----------you can make individual strips from just a few inches to however long you want-----------cut only after you've sewn a few strips end to end. When complete, they'll be sort of willy-nilly when sewn together.