Our's is about 1000 sq ft on the main floor with about 400 upstairs and a walk-out basement. The cat owns the loft, The two of us and the dog share the rest. The gunsmithing shop is in one end of the basement, a hair dressing shop in the other, with the middle disputed. We have three bedrooms (one is in the loft) 2 bathrooms (one in the basement), and an exercise room with weights, a heavy bag and speed bag.
Not anything fancy but I built the whole thing myself. I dug the hole. I mixed and poured the concrete. I did all the carpentry, wiring, and plumbing. When it's 20 below outside, I'm warm and comfy in here; as long as I keep feeding the fire! I have a 28x 48 shop which I hope to finish before I check out. I won't build another one but, if I should buy one, it will be about the same size. GD
