To the OP, no not really. If a character is willing to invest the time in it then there is no real limit on the amount of power that he can pour into a ritual; and if he is willing to only invest Discipline-4 points shifts of power into the spell each exchange of casting then he has no chance of failure. This being said, if you are casting an 8 hour long ritual then you better be sure you have your Endurance high enough to cover things like "has to shit" "has to eat" "falling asleep" etc.
In game terms a ritual has one real limit; it's complexity. Pushing complexity up isn't particularly difficult but it takes time, potentially a whole lot of time. The other way to push up complexity (and the fastest method) is to break the Fifth law and use sacrifices.
In terms of the narrative rituals have two inversely proportional parts; the complexity, specificity, and control of the ritual and the power of the ritual.
Take Storm Front, Dresden says that performing the heart ripping curse is at the very limits of his power and skill but when he finds out what Sells is doing he changes to "oh, that is really simple". The difference here is the available power. If you have tons of it then you can cast a ritual that doesn't involve any of the tricks that make it far more efficient or require less raw power.
So for high complexity rituals you either need tons of power from an external power source or tons of little details that reduce the power required significantly.
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Remember, as we are shown in Changes, the only actual requirements for any magic are 1) a symbolic link, 2) power, 3) the ability to control that power. All of those physical items in a ritual and other external factors are a stand in for one of those three things.
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The other big constraint, in terms of the narrative, on high complexity rituals is the various powers of the world. When you are talking a 200 complexity ritual that is an amount of magic that any supernatural within a hundred miles will notice pretty much instantly. At a minimum you will have Wardens dropping in on your head in minutes to figure out just what you are doing casting a ritual more than powerful enough to obliterate an entire city. Every other super natural power in the world will also suddenly become interested in you and what you are up to.
If you want to get around this then you either need to go the route of mass necromancy and sacrifice a few dozen people (enough to cover the complexity, enough to power the ritual, and enough to eat the backlash from casting the spell in one exchange) or go the route of lots of time and preparation work.
Instead of necromancy you could put up a ten shift ward around the ritual site which will then conceal the casting of a fifteen shift ward behind it (only 5 shifts leak through the first ward) which will then conceal the twenty shift ward which will then conceal the twenty five shift ward which will then conceal the thirty shifty ward, etc. until you have enough wards up that the inner one is strong enough to conceal the power of the ritual and enough to step the wards power down so that people don't say "why do you have a two hundred shift ward here".
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As for how you go about doing this, you stack rituals. A lower complexity ritual is used to provide aspects that can be tagged for a later ritual which in turn can provide either still more aspects to tags or increase the duration for which those taggable aspects will hang around. Eventually you can built up enough of a pool of tags to cover the complexity of the ritual that you wanted to cast and potentially even the power and control of the actual ritual. It's just taken you six months to a year of constant work instead of a few dozen bodies and a few minutes of work.
If you put in the prepwork though, you can far exceed the power of necromancy without breaking any of the laws. It just takes a very long time and a lot of prep work.