The latest issue of The Family Handyman has a beautiful house on the front cover that happens to be step-by-step plans on how to build an Arts & Crafts style shed with a front porch. I think with a little tweaking, and the installation of electrical and plumbing, it could make a very nice tiny house.
This particular shed is 8×16 feet with a large sliding door on the back that runs on a track, three windows that let in plenty of light and a front door with a wonderful front porch that brings the total area of the shed to 16×16 feet. The structure can be built in four or five weekends with the help of a few people. The cost (not including the concrete slab) is about $3,800, and the skill level needed is intermediate. Experience with framing is helpful, but not necessary. Because of the sliding door (that opens up the living area) this structure will probably work best in warmer or milder climates.