The rules do not say. There are two schools of thought here:
Up to the lunar sphere, down to the centre of the earth.
Within a sphere whose equator is the ring.
Yes, althouth if you adopt interpretation 2. and the building is tall and slender, and the ring is too "tight", you might leave the upper floors out.
The general consensus is that moving rings should not work. Several people seem to be willing to make an exception for rings that are static relative to some pretty large moving object, such as a ship or flying castle. Few people are willing to accept rings on small movable objects, like bells or crates. Very few people are willing to accept tiny moving rings affecting anything "wearing" them.
[quote="ezzelino"]
The rules do not say. There are two schools of thought here:
1. Up to the lunar sphere, down to the centre of the earth.
2. Within a sphere whose equator is the ring.
[/quote]
All the canon "wards vs faeries of the ___" are clearly described of the sphere type, but some SG's/Troupes interpret other rings as infinitely high cylinders - but I'm not sure there is any canon support for such. If not, then it's just convenience and intentional memory lapse, so that "ring" effects can block a square hall or encompass a tall tower, etc.
[quote="GribbletheMunchkin"]
If i cast the ring around a building, it makes sense that it would affect the whole building.
[/quote]
Another limiter is the actual drawing of that ring - Concentration rolls/etc. Even if using a pre-fabricated physical ring (of stone, of metal, magically carved, etc) that only helps the drawing - the ring must still be physically, [u]manually[/u] drawn (houserules and Hermetic breakthroughs aside).
I like to go with the sphere myself. And it makes it easier when a clever magus traces a ring on a vertical surface: that still creates a sphere, no problem.
I like the sphere as a default, but I also like the idea of a column when a ring is inscribed on the floor (or ceiling) of a reasonably-sized room or hallway. I think both could be possible in Hermetic theory - at worst needing to be fixed at spell design.