I designed and built my own little house. Actually I hired a professional carpenter to lead the construction and I provided assistance and learned a lot. The two of us did everything except plumbing, electrical, insulation and drywall.
My house has 584 square feet of interior space, plus 120 square feet of porches. The two-story house has just four rooms - living room, kitchen, bedroom and bathroom. Here's the floorplan for the first floor, and for the second floor.
There are many more photos of the construction of my house for viewing. Construction took about 9 months because we were slow and figured out the details of the design as we went along.