Currently, if you try and set a PBR material on an old build, you get an awful blueish hue reflected on the reflective parts (e.g. metal), due to how the sky gets reflected on them, even from inside a building.
For now, the only solutions are to:
  1. Enclose the building with a reflection probe primitive. Fine, when you can do it, and when the building is less than 64m large in any of its dimensions...
  2. Add a reflection probe primitive to the linkset of the object you use PBR materials upon to enclose it: fine, if you can modify it, and if it is not scripted in such a way that would break its scripts when adding a new primitive to it (sadly, a common occurrence).
  3. Add a stand-alone reflection probe prim and place it (without linking it) around the object(s) you want to shield from the sky. This will work almost always, but supposes that you move or resize the probe manually when you move the objects, and that the objects themselves are not moving on their own (scripted objects, vehicles)...
All of the above is rather user/builder
unfriendly
.
A simple alternative would be to add a property to the root objects for any existing linkset, that would flag the whole object as needing an enclosing reflection probe; the server would then transmit this property to the viewer among existing object properties, and the viewer would compute (it already does anyway) the bounding box of that object and automatically add a matching reflection probe (of the "box" type) for it.
That property would then be made available as a check box in the build floater.