When I was a small boy, we made a few trips to visit my paternal grandparents in southeastern Colorado and went out of town about 20-25 miles to the original family homestead and were shown the remains of the house my father grew up in -- a genuine sod house. The house (completely gone except for parts of one wall by 1970) was built sometime just after 1900 and my grandparents continued to live in it until sometime around 1940-45.
I wish I had more memories of that sod house from when we visited it, probably around 1956-57, but I really don't. You must admit, though, from my vague memories of the structure still standing then, that it was put together pretty well for something built of prairie grass and Colorado/Kansas mud!
The house was actually located almost exactly on the Colorado/Kansas border. My grandparents' homestead split along that state line. As I recall hearing the story, the house and well were in Colorado and a shed and barn were in Kansas. The whole site was somewhere around 20-25 miles north-northeast of the small town of Holly, Colorado. Holly made national news a couple of years ago just briefly because a tornado ripped through the little village and wiped out a great deal of it.
Back to the sod house. I found a very good description of how the early settlers in the Plains states put these structures together. It's in Foster-Harris' book, "The Look of the Old West," on pages 280-283. If you've been fortunate enough to find a copy of that wonderful book, you'll see the same section speaks of the early dugouts that preceded sod houses, and a brief description of the ranch houses which generally followed as a step up.
In our family's case, my grandparents moved into Holly and left the old sod house behind sometime in the early- to mid-1940s. My father was an expert carpenter and woodworker. He hand-built, from digging the foundation to shingling the roof, a house for his parents in Holly then and they left the homestead behind. (According to my grandmother, who was very bitter about it all, they had spent 30 years too long on the barren land outside town as it was.)