The answer to this is easy: it depends, so beware of builders who advertise and quote square foot price.
As they say, “actual price may vary”. In order to accurately quote the cost of a house you need to examine the entire project including lot, amenities, plan etc.
If we are doing a lot of expensive upgrades it is obviously going to cost more than if we did cheap amenities.
Size is also a factor – the larger a house is the cheaper the square foot price.
The most expensive square foot in your house is the first one because there are a lot of fixed costs in building a house. If you are just adding square foot to bedroom, that will be cheap. If you are adding another bathroom, that’s going to cost more per square foot.