No it is a full size room on the east end of the barn. Fortunately I didn't have to add it. There is the main portion of the barn, and then another room on the west end. Plenty of room for me in various pursuits.
Hmmm removing the roof in the summer. That's kind of tricky. Amateur astronomers do build small observatories with roll off roofs. https://www.google.com/search?q=roll...w=1920&bih=944 These might be too extravagant for your needs. You said largish tent, what size are you thinking of? Have you considered a Tuff Shed? https://www.homedepot.com/services/...tUACc5-r5IHyTfwi6yxoCIfsQAvD_BwE&gclsrc=aw.ds You would have to insulate it though.
That observatory is pretty cool, for sure. Not sure I was imagining anything more elaborate than just a large enough door/flap to let out enough so that things don't bake if I ran it in the summer.