These answers may help me in my similar dilemma. Although my sewing supplies are scattered all over the three story house, my primary sewing room is upstairs in a former guest room. I have one southeasterly window of which the drapes are almost always closed. This is my largest stash area, so I don't want to fade the fabrics with the flood of light. I use full spectrum florescent lighting, but open the drapes on rainy or cloudy days.
The question I have is to build a storage building for all the "stuff" in the basement, and consolidate my sewing down there, or build a sewing cottage. If I build a cottage, I want a small kitchen and laundry, suitable for hand dying, and half bath, which means a new drain field. However, everything would be in one place, on one level, (not 3) and I'd have natural light which seems to be important to the lot of you.
Thanks sunni for asking this question.