Chasing Hawks Ideas are good for the walls. Insulation will be a key factor in your comfort. Instead of heavy drywall, though, I would get some inexpensive paneling and put that up. That's much lighter in weight and therefore more manageable as a do-it-yourself project. Around the windows, get some insulbright or foam insulation and wrap it with fabric, then fasten it around the windows as a frame. Make sure you like the fabric as it will be there as long as you use the garage for your sewing room! You could even get a fabric that looks like wood grain, which would make it less noticeable.