Hi everythingape, I'm a quantity surveyor in the UK (local authority).
Your outline design looks fine but more detailed working drawings would be required in order to properly cost this project. Having said that - if this concept has been built before then you already have a step for a hint regarding the cost.
I don't know how building costs in Norway compare to the UK and also in the absence of any materials information I could only give you and indicative cost to build this in the UK.
We’re looking at a floor area of approx 260 sq.m. (not including garage). Also not including land preparation (there’s a hint of cutting in to a hill on your sketch) I’d say you’re in the region of £100,000 - £120,000 to build.
If you were to build it yourself then this will reduce labour costs considerably but plenty of blood sweat and tears.
JTB