A Shirtdress seems to be one of the most versatile pieces in the wardrobe. It will serve you as a dress, duster coat, top, tunic and skirt. Here are some ideas of how to wear it.
I would recommend a shirtdress made from flowy but substantial fabric. For example, lyocell, viscose, weight silk and chiffon.
The simplest way is to wear a Shirtdress as-is
The next level is to wear it as a Duster-coat
Try it under a sweater or vest
Play with layers
Or why not to try a shirtdress under a skirt
And here are a few more pictures for the inspiration
Anything you want to try? :)