I did a good bit of television work last year at the Norwegian folk museum in Oslo and at the Maihaugen open-air museum in Lillehammer, both of which can help you in the sod roof department. Basically, you need heavy framing, birch bark, and sod on top. A fine book to help you, is "the Craft of Log Building" by Herman Phelps, published by Lee Valley tools of Canada. Excellent on how to frame for sod roofs. Will dig up numbers for Norway somehow. Good luck. Roy