I love this idea and is totally doable and sensible. Why have your man cave attached? When it could have its own zip code. Awesome mancaves made from old sheds and other similar small buildings.

Love this! Reclaimed wood shed: wow.Wood from three old Oregon barns now makes up Megan Lea’s Backyard House, a 154 square foot studio with loft. Quartertwenty was the builder for the project. would make a great guest spot

Build Your Own Simple Shed - Popular Mechanics

Build Your Own Simple Shed From Scratch