If not, what is required from the owner of the building to have the rights to sell scale models of their buildings?
For the US:
I believe 17 U.S. Code § 120 applies here:
17 U.S. Code § 120 - Scope of exclusive rights in architectural works
(a)Pictorial Representations Permitted.— The copyright in an architectural work that has been constructed does not include the right to prevent the making, distributing, or public display of pictures, paintings, photographs, or other pictorial representations of the work, if the building in which the work is embodied is located in or ordinarily visible from a public place.
So long as the building is located in or visible from a public place, anyone should be allowed to distribute models of the building
Edit (more information, but I believe original answer still suffices):
So we know from 17 U.S.C. § 102(a)(8), that architectural works are copyrightable, and the extent of this copyright protection extends to copyright over the blueprint itself and/or the right to produce the building.
This seems to only mean that an architect would own copyright in a model of a building if he specifically creates a sculpture of the building and then copyrights it. It doesn't appear that designing a building or having blueprints of it grants the creator rights over a sculpture of the building, the rights to such a sculpture would have to be obtained seperately.
TL;DR You should be allowed to sell models of a building so long as they are not models based off the actual blueprints of the building, and that these models haven't been manually copyrighted by the architect beforehand. (i.e making the building hasn't granted a copyright over models of the building beforehand)
Assuming US (copyright) law, it depends in part when the building was designed and built. There is no protection for buildings constructed before December 1, 1990, or where the plans were published before then, or were "unconstructed and created in unpublished plans or drawings on December 1, 1990, and were not constructed on or before December 31, 2002". In case the building is under copyright protection, you would have to determine who holds the copyright. That could be the architect, or the construction company (the architect might design as a work for hire, for the constructors, or it could be whoever hired the construction firm. The current owners might be the rights-holder, but they might not (and they might not even know). Once you determine who holds the right, you can ask for a license.
That said, I think that the external appearance of a public building is not protected. 17 USC 120(a) says
The copyright in an architectural work that has been constructed does not include the right to prevent the making, distributing, or public display of pictures, paintings, photographs, or other pictorial representations of the work, if the building in which the work is embodied is located in or ordinarily visible from a public place
A scale model is reasonably interpret as a pictorial representation of the work. The wording "if the building in which the work is embodied is located in or ordinarily visible from a public place" is a bit hard to parse, but the idea is that "the work" is the thing that the architect made, and the final building is the embodiment of the work, so then the question is whether the building is ordinarily publicly visible. However, I do not think this means that you can create any old derivative work off of the original drawings. Assuming you can't get your design from the visually evident (i.e. computing distances between windows, other dimensions), you have to refer to the (protected) design.