Hi everyone. As the newest addition to the troupe, I feel like I'm the least qualified to comment on this discussion. But if my perspective can help find a resolution, then I offer it in that spirit.
I'm sure we all agree that we want to enable SGs to focus as much time as possible on story content. One approach to get there, that you mention Arthur, is to implement SG fiat. But I don't think that will work well long-term - there's a great risk for the accumulation of frustrations that leads to player turnover. I feel similarly to Gaxxian that it's important to hash out differences of opinion/interpretation on the rules, and align as a group to keep everyone engaged. The only potential antidote I've thought of so far to rules discussion burnout, is to share the effort across more people. A Judge/Lawyers approach, to mimic Gaxxian's Judge/Jury description. Not with the intent of diluting your authority - the Alpha SG still gets the final say, especially if there's a gap in the rules or we can't come to a consensus. Could that work? Provided we are thorough and focused on finding a well-supported solution?
For the specific spell design issue at hand, I think there was unfortunately a derailing early on caused by a math error. Here is a table of how size modifiers scale the volumes of stone structures, using 1 pace = 3 ft = 0.91 m, and with 10X factors applied to the base individual size of 1 pace^3.
| Size Modifier | Volume (pace^3) | Volume (m^3) | Volume (ft^3) |
|---|---|---|---|
| +0 | 1 | 0.8 | 27 |
| +1 | 10 | 7.5 | 270 |
| +2 | 100 | 75 | 2,700 |
| +3 | 1,000 | 754 | 27,000 |
| +4 | 10,000 | 7,536 | 270,000 |
| +5 | 100,000 | 75,357 | 2,700,000 |
| +6 | 1,000,000 | 753,571 | 27,000,000 |
A bit of a tangent: The "clarification" about how size of a target should scale with mass is actually in the core rules (see 2nd paragraph in Targets and Sizes box on pg 113. But I think they shouldn't have introduce a different way to measure size here. The example they give - that a +1 (5 level) boost to a Corpus spell allows it to affect a giant that is 15 ft tall (and presumably of larger than +0 girth), not 6 x 10 = 60 ft tall (if a +0 human is 6 ft tall) - suggests that all 3 dimensions of an object are meant to be included in the scaling. But I don't think we need to apply that limit to every Form or situation. Similar to the question about dome area, as long as we take the consequences of medieval physics into account, we should be able to scale dimensions arbitrarily for some things. For example, why couldn't you make a wooden plank that's 10X longer than the base individual plank, but has the same thickness and width, if that aspect ratio is strong enough to persist? In any case, I suggest that we stick with scaling volumes by 10X for each factor of +1 as done in the table, since the sizes of base individuals for most of the Forms are given units of volume, not mass.
According to one of his posts, Gaxxian's structure has a target volume of 650 m^3, so, interpolating within the table, it should require a size modifier of +3, which I think was the original proposal. This spell would theoretically allow creation of a structure that's up to 750 m^3 in volume. So a full reckoning of the spell would be Level 25 (base 3, +0 Momentary, +1 Touch, +3 Size, +2 Complexity for a less exciting design with few internal rooms). Do we want to apply a Finesse check to see how lopsided the dome turns out to be? 
Using the same approach for the structure created by Conjure the Mystic Tower, it has a volume of 90k ft^3 if square or 70.7k ft^3 if circular. So it needs a size modifier of +4, since the 27k ft^3 from +3 are not enough. Can a magus invent a version of this spell that makes a 270k ft^3 structure with the same +4 size modifier? I'd say yes, that should be allowed.
Another, more obvious tangent: Conjure the Mystic Tower creates a tower that is roughly as tall as this one, but about half the diameter. It's hard to get a good sense of size from just the numbers, at least for me, but the image helps drive it home. I think it is quite a large structure for the middle ages. Huge even. The standard sanctum and lab, according to Covenants (which I'm not sure if we are using here), fits on one floor if such a tower (~700 ft^2). If the standard sanctum + lab has a ceiling of 10 ft, and therefore a volume of 7000 ft^3, Alba's lab is going to be big enough to fit almost 4 of them. I'm providing these numbers for a sense of scale, and to compare to what other magi will have. It may not be a reasonable expectation for a maga to be able to create something so big, only 5 years out of gauntlet and with apprentice-level CrTe Art scores (Cr=6, Te=1, in the latest sheet; sorry if I missed CrTe advancement that you were already planning to do). And even if the structure-creating spell is designed properly, and if Alba's Art scores are high enough (or will need time to increase before she can invent/cast the spell), will there be any consequences to having such a structure appear on covenant grounds?
In any case, I hope very much that the saga will carry on, and am open to helping in any way I can.
And this is just 1/3 of the total problem.
It's not fair from your part.
