in the AM5, pg 112, Ring Duration is defined as "the spell lasts until the target of the spell moves outside a ring draw at the time of casting, or until the ring is physically broken."
If a room is circular, can you cast a D: Ring spell with T: Room, and have a spell last until the room falls apart? or does "physically broken" mean that if someone enters the room, the ring is "broken"?
I'd like to cast a CrIm spell in the room of a tower that makes it feel like it's a different location. For story reasons, I need the spell to last longer than a year. I'm wondering the best way to achieve this. If not the above method, then I guess an enchanted device that auto casts the illusion at dawn or something...?
This would require making the walls of the room into the ring - hence drawing the ring by building the walls. That's many, many easy Concentration stress rolls during their construction. And if - by an incredible streak of luck - this succeeds, opening the room's door could break the ring.
That is certainly more plausible.
If you cast Ring spells for long duration, you need to plan the occasional repair. If you inscribe the Ring onto the floor or wall of the circular room to create a cyclorama (like en.wikipedia.org/wiki/Gettysburg_Cyclorama ), prepare to recast the spell if mice, cobwebs, falling plaster or careless visitors have broken it.
The phrasing of the Duration: Ring text is unclear in several respects. Notice that the text doesn't actually say that the target needs to be within the Ring - arguably, the spell can be cast with the target outside the ring, and will then last until the target enters and then leaves the ring (or the ring is physically broken) - but that's clearly not the intended meaning, so you might want to forbid that.
How about a ring drawn around the target, and then a hair falls over it? Is the ring "physically broken"? Arguably not. But if not - what about a ring covered in dirt? Is it still active? If so, you can cast the spell, and then build the room on top of the ring.
And how high does a ring affect reaches, anyway? If I draw a ring on the ground, does it extend to protect a giant standing in it? No matter how tall? And downwards, to the center of the Earth? If so, perhaps enchanting the floor of the room, or the sides of the room (above the doorway) is enough to enchant the whole room.
I personally think that rings should be visible, so if enough of it is covered the spell will fail; thus a hair won't break a ring, but you can't cover-up a ring and build on top of it. I also think that rings should be on the ground, affecting things above them - thus you can't place the ring at mid-level in the room, above the doorway. On the other hand, I do think it's quite reasonable to have a lead "ring" tracing the inside rim of the room, which allows casting Ring-duration spells that affect everything within it. None of this is quite what the official rules say, or not say. You have to decide how you want to do things for your own saga.
Notice that if you want to actually affect the room itself, rather than what is in the room, then my "inside-rim" solution won't work. A constant-effect enchanted device (activitating every Sun, as you say) is the way to go there.
Personally I would allow the ring to be the first layer of blocks above the floor level (assuming a stone wall) then build the rest of the wall on top of this. Of course you will have to have that wall built with the illusion in effect, and if the bottom ring gets damaged in construction the spell ends...
A troupe asks for problems, if it allows everything that roughly defines a circumference - like walls, stairs up a podium or altar, window and door frames, rims of chalices or buckets, keyholes, holes in clothing and so on - to be an already existing ring.
I would say that as long as it is the object itself that defines a ring, not just a geometric aspect of the object (for example, the rim of a chalice or bucket is not a chalice or bucket, but a metal band around a barrel is)