What is the estimated cost per square foot to remodel a custom home in northern California?

It varies from builder to builder. On an average, for a mediocre house, with decent raw materials, have 1,000 US as a base price in mind. This looks like a typo. $100.00/s.f. would be more like it.

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$1.00 per square foot

That depends on where you are building, who is doing the building, the amount of add-ons (the fanciness of things such as cabinets, plumbing fixtures, flooring etc.) If you already own your land,...

$40-80 a square foot is not uncommon for remodeling, with $120-150 a square foot for new construction.