It is difficult to build a sauna. If you can and want to build, then I think you'll like it. My husband loves all these DIY projects. I recently built a small barn in my garden so that I could put tools, seedlings and decorations for the holidays there. Now on the Internet you can find any plan, any advice on construction and repair. Most likely, you need to replace the roof in the extension. The roof of the sauna must be installed under the stove. You can look up information on the internet, here
myrooff.com It's a lot about ceilings. In any case, I wish you good luck and good construction.