I agree with Dunster. The housing is too small, quilting in a shed is boring, and what will be the attraction for attendees? I would think a retreat area needs to accommodate at least 20 guests (or larger) and the necessary staff. A big bright room for quilting is needed, but it must be accessible without going outside, needs windows and ideally view. After quilting all day, I want a break and would enjoy a peaceful walk. What is the scenery like? How close is the nearest quilt shop? If it is not convenient, then basic quilting necessities would need to be offered for sale. I don't think a business can exist as only a quilting retreat. Are there plans for other uses like family gatherings or business meetings?
Personally, this idea sounds more like the person wants their own personal quilting retreat and are trying to justify it to their spouse.