That was kinda my thinking when I thought of a shell keep. It is definately not what you would usually think of as 'wizardly.' I liked the idea of an enclosed courtyard. But I'm at a loss on where else to go for ideas on 'different.'
Isn't the Tower spell a Lvl 50 ritual or some such? Not near my books.
If Agitatus can cast that level magnitude, his Terram is probably up there. Maybe instead of CrTe we could ask for a PeTe (Caves) or MuTe (change up some existing structure like a hill)
The tower is actually fine with me. But Kerry brings up a good point about hosting the fair. We'll need some type of courtyard or large space to hold the fair. Preferably out of the way of mundanes (although being close to civilization and holding the fair would present an enjoyable challenge).
Two towers for us and then large courtyard inside the walls we can put all sorts of buildings around the courtyard for gues quarters and such.
I suppose that works... I LOVE repurposing old ruins and existing terrain. Magi are original and quirky types, and the fact that most covenants wind up feeling like apartment complexes is, to me, a downer. If your character really loves a tower, bully for her, but I'm completely sick of magi living in the same copy-pasted tower complexes from Ireland to Byzantium. Why can't we be in a regio, or burrowed into the side of a mountain, or even in a small, walled town, with every magus having their own house? Why is it -always- towers?
See for me, I have never yet had a mage live in a tower. Cave complex once, building to herself for two sagas, no lab yet for a fourth one. I have yet to do a tower let alone a magically summoned tower.
Hmmm... what if he did a Conjure the Mystical Town instead of tower? This makes strong, thick, high stone walls with a defensible gate or two, periodic towers and buildings inside. Herbam requiste for roofs, doors, etc. You could make the houses out of stone or wood. Just make sure there is enough room in the town center for an open courtyard for the fair. The first 'Hermetic Town?' Aura couldn't be more than 5 in the town though.
How big a town would that get us?
Honestly, as big a town as QC would want us to have. Conjure the Mystical Tower is a 35 ritual. If this guy is as old as he claims, then something larger shouldn't be an issue. If going strictly by the rules, CtMT has a size +4 modifier in it, which means 10,000 cubic paces of stone. +5 is 100,000 +6 is 1 million. As long as all the buildings touch each other, then I would think you could keep Target as Individual. So just bump some magnitudes for size.
Pros and Cons then:
Tower: More of a defensible structure I'm thinking. More control over who gets in and who gets out. More foreboding: might keep the peasants away.
Town: More spread out so we're not on top of each other. There would possibly be more room to individualize your magi's space , Town is going to be more "inviting" so we would have to deal with a lot of visitors (good or bad depending on how you look at it), less defensible.
I can see a fair working with either setting, though the town might work out more easily (but then who wants to do things the easy way)
What other pros/cons am I missing?
A town might be more political. I believe towns are run by councils, but since I don't have the book in front of me, I could be wrong. Towns also attract guilds and the church. Trying to keep the Divine aura in the town down might not be easy. Would have to put labs in a Regio, underground, or get some Hermetic Architecture. 
There would be a lot of working behind the scenes so as not to be seen as meddling.
On the other hand, if you considered all the town within the wall proper to be part of the covenant, then we could probably get away with more direct interference.
I don't mind visitors. Visitors mean money. Oh, and stories.
Wow! All this talk, glad to see it, but this is really getting away from the original plan. But that's OK, let's go with this a bit.
The town thing is actually representable by some boons and flaws and is also doable by the characters. Agitatus can raise a tower, and Rhodri actually knows how to build houses with magic. He doesn't have a spell that just builds the house, but he has The Mystical Carpenter and a specialty in finesse. He can actually put up houses rather fast.
This could be represented by the Magical Fortress Boon and the Outbuildings Hook (which basically means a bunch of wooden houses around the main structure).
Creating a town isn't quite as doable, what's more preferred is the villa concept, with a main structure and then peasants working the land around it.
OK, also since the tie breaking vote was not cast for whether or not the Covenant was secluded, I will be casting that vote. I will have the Covenant more secluded. This means it's more than 10 miles (at least) from civilization. The area that I have in mind is so open, it is more likely to go for a more secluded spot, and if you're having a fair most would appreciate less Mundane interference.
Let's keep the Covenant talk going, I'll move the Tribunal along.
Surefoot added his vote today to go with Max.
Woops!
Very well then, I will ammend it and we'll have it closer to civilization.
OK, so we will work with the tower idea. Do we want two towers full of magi, or one tower and the remaining magi in seperate wooden structures?
Stone is more resistant than wood for magical mistakes in the lab, but the tower lab cannot be made larger. I could see Bjorn using a wooden building, then he has room for the tools of his trade, wood storage, and a studio along with a lab.
If you were to use the two towers option (there's a perfect picture of this in Heirs to Merlin on page 126, that's the Covenant of Nigrasaxa and is in fact two Wizard's Towers joined by bridges, the tower that the wizards inhabit doesn't even have an exterior door on the ground!) that would provide the full Magical Fortress option. Two defensible towers with an abundance of room. You could in theory have all the wizards in one tower, labs sanctum and all (it'd be a bit tight). The second tower could easily hold the grogs, spare rooms, and specialized rooms.
If you want to have the Outbuildings hook that's fine with me, I can always replace what I had picked as a Hook to pay for the Fortification and Aura bonus.
The main thing still comes back to what you want for the Magical fortress. It doesn't have to be a tower above ground either. In the adventure Broken Covenant of Calebais it was basically a reversed tower, the spell they cast created a tower that went into the earth. That's a perfect example of a magical fortress IMO.
So could a single, larger tower be underground (or two towers, doesn't really matter) with just a hole and trapdoor as an entrance? Then we could build a wooden building over it, and have the grog population make their village pretty much on top of the covenant. This would also give the ability for later expansion by just digging a hole in the wall.
Or another thought...
Would a really high wall around the tower and grog buildings (envision a shell keep with a tower or two) count as magical defence? Perhaps more importantly, could it be done? I see the 1-2 towers, and wooden buildings being constructed on the inside face of the wall. This would give the added bonus of a large, enclosed courtyard.
If we make it the towers (up or down), we could have the stairs in the center of the tower and instead of a stairway, there is unlimited use ReCo enchantment to cause people to raise or drop slowly (entering central tube triggers it). At each level there is a rope across the middle to pulls yourself over to the door. (level 20 enchantment, ReCo 10 + unlimited use 10)
I like the ReCo idea. Perfect for a Verditius. I would prefer a stairwell or two on the sides of the tower, only so we don't have a large dougnut shaped lab. Though I don't know how well a stairwell would fit on the side. It would be another reason to put the tower(s) underground though. Then you could just dig a shaft next to the towers.
Underground towers would also lessen the attention we would get from mundanes. I think the idea is growing on me.
I'm thinking a sumna on Muto L: 11 Q: 9, and an Aegis L: 20 for my build points. This leaves me one left. I'm still thinking on it.
The underground version would then make your fortification much less conspicuous since you're closer to civilization also.
There's plenty of expansion opportunities also that way. I'd have to re-think the Hooks I had in mind most likely, but that's OK.