You want the area to be dark so that your colors will be preserved at their optimum peak. You want it to be cool, to prevent moisture and mildew. Mildewed plants must not be used in craft projects. The more air movement you have, the better. If you decide to use a shed, think about setting up a fan to help circulation.
Some people suspend their bundles from coat hangers.
This makes it convenient to hang them anywhere. Make sure your stems are hanging straight. Once they are dried, they will break if you try to straighten them. Some people don't mind if their stems are bent. They incorporated the natural flow of lines within their designs.