According to you, what defines a building?
what defines a building is the plan.
I'm not sure I'm interpreting the question correctly but I'm concluding you are trying to determine: At what point can a built structure be defined as a building rather than an accessory structure or other built entity?
We recently had this discussion when working with a design review board of a small municipality in trying to determine what structures were actually regulated by the unique zoning code that regulated a particular property within the township. The way theis particular code was worded was that it pertained to "buildings" on the property.
My argument, and it was accepted by the commitee, was that a building was a structure or built entity that enclosed an occupancy. In this instance, we were not required to conform to certain aspects of this particular zoning code for structures or other built improvments as long as they were not intended to enclose or define an occupancy as defined in building codes.
FIRST AND FOREMOST - FUNCTION
THEN THE - FORM
@ Sattanathon - I agree with the function vs. form. At a fundamental level all designed and created things are defined by their function. That can be applied to everything we design; spaces, buildings, cars, hell - even a toaster. When designing something, I start with the function, but as the design develops and forms emerge, the function and form can no longer be separated. The function, form, and all characteristics the design takes on become part of it's definition.
Literally, if you define a building it is: "Any structure used or intended for supporting or sheltering any use or occupancy." - 2009IBC
If the question ws meant more abstractly, then you get into feelings, emotions, energy, etc. This is much more subjective and therefore more difficult to simply put a definition on.
If you try to born a debate regarding form and function:
The function is the sine-qua-non reason a building exists. Regarding the form, most of the theory understand it as an appendix and most of the time is a line in the sand regarding where the Architecture is not just construction.
I understand the aesthetics of a building as another function of it: all buildings have inherent communication activity whenever this is controlled or not. As a court of law shows most of the time imposing classical features revealing its importance in the society, the same way a house is somehow as the Facebook page of its owner.
The aesthetics of the built environment also have a huge impact on our psychological equilibrium helping grow comfortable feelings, challenging feelings, tensioned feelings. We like or dislike architectural spaces.
How the design effort should be focused more on the aesthetics functions of a building is another question: My short answer is that each building has an importance level that requires more or less aesthetic involvement, sometimes on the expense of other functions.
But I think there are many occasions when the architecture must bu humble, as the white rooms of the art museums are designed to exhibit the art, not compete with it.
So...that is why we are architects, right? To use forms in the pursuit of functions.