The factors affecting this answer include:
- Topography of the homesite (flat vs. hillside)
- Quality of the surfaces and construction (e.g., marble vs. tile, 6" wide studs vs. 4" wide studs, etc.)
- Skill of Project Manager in getting a job done in a timely manner
- Change requests by the Owner
- Costs of materials and labor in the county. (Marin is one of the more expensive places to build.)
That being said, an overall guideline might be...
- Low quality, flat lot....$250-275/sqft
- Medium quality, minimal grade to lot....$300-325/sqft
- High quality, and/or more severe grade...$350-500/sqft.
An additional source for this information would be a working architect. Hope this helps!