How big does a house have to be to be a big house?

I consider anything under 5,000 sq. ft. a "good size".  Over that is big.  My house is 2,400 sq. ft.  I consider it modest.  Nice but modest.

It should have at least three bedrooms.

Depends on the person looking at it and their needs. 

It obviously varies from place to place but I'd say that anything over 2000 sq ft is pretty big.

That is subjective to what YOU think makes a house "big".

Is "big" based on number of bedrooms.

Is "big" based on size of the rooms.

Is "big" based on the square footage of the house.

What I think is "big" might seem "small" to someone else.

Obviously that’s subjective, but I think most people would not consider 3 bedrooms or less to be big.