If you’re wanting free heated space for activity a low thermal mass attached greenhouse is great!
https://www.builditsolar.com/Projects/Sunspace/sunspaces.htm
I can sit buck naked in mine after 2 - 3 hours of sunshine even when the outdoor temps are in the teens.
Not much good for plants though as they get too warm in the day and too cold at night.
That link was a disappointment considering your description if it’s abilities.;)
link for later read