It's probably a magnitude too high for spontaneous casting, which is bad. I'd be interested to hear your opinion though if this would actually work.
The problematic parts I see are the different durations, the Muto part should be ring, the Perdo part momentary and what happens if only a fraction of the clay gets carried out of the circle.
Separating this into too effects would have a major drawback, the Muto effect would probably have to target part instead of circle and add a magnitude or two for size if the site should be cleared for anything bigger than a hut.
or not even a circle, once you are removing a homogeneous material it is simple and quick to just blow away Individuals worth of extra material (spontaneous so you would assign extra mags to size.)
Next problem after dry building site or even before... How to get all those stones there...
Keep in mind MuTe and ReTe are good enough for spontaneous 10 (or maybe 15), that's much less then I like and most options are out of reach, though some only slightly...
What do you think is a good size for an initial covenant for 4-5 magi? I was thinking we might start with only about 300 square pace (which means only a single shared lab) and extend from that. Even that would mean a lot of stone though I fear...
Yeah, but which...
There is Muto "Change earth so that is highly unnatural." that is lvl 4,so 5 for stone. +1 touch, +1 concentration an we hit the limit. A potential quarry is a days travel from the covenant site, unlikely to keep concentration for that long, and even if... It's one cubic pace of 100s we would need...
Then there is Perdo "Destroy one aspect of dirt, such as its weight", that's 5 already so 10 for stone and we are still not on touch range...
And Rego "Control or move earth in a very unnatural fashion.", level 3 - so 4 for stone. +1 touch +2 day for 15...that's going to work sometimes, not always and a good chance to botch for every cubic pace... And then unseen porter uses the same base (my magus even knows that one) and that has" Roughly speaking,it has the capabilities of a very strong person(Str +5)." which doesn't sound like it could carry that one cubic pace even...
For whatever solution you go for that involves spontaneous spells, a Sun variant of Maintaining the Demanding Spell really helps to make them go the extra mile.
Last time we had a covenant controlling a quarry, we made that a source of income: quarrying with MuTe/ReTe magic, selling the good stone to people building churches, castles or such, and using the leftovers to MuTe-cast pillars and foundations of buildings for the covenant.
As the good stones had to be transported to the 'mundane' construction sites, we had lots of teamsters to handle that. These also brought the leftovers to our covenant site. We had no covenant in a swamp: but transport by barge - if the swamp allows it - would be easier than the transport by wagon we had organized.
The other option is to forget all this heavy construction for a starting covenant, and use your Architecture skill to build wooden buildings (maybe a manor house, maybe a tower if you want fortification) - they're a lot less heavy so you don't need to worry about the foundations as much; the materials are easily transportable and there's probably some local forestry nearby to source timber from; they are less threatening to nearby nobles.
You can then proceed to study your Arts and research spells in the lab for the covenant of your dreams, while trying to build sufficient relationships with nearby people that they aren't surprised that you've upgraded to a stone building one year.
I don't think anyone's suggested this yet, but you could do a surprising amount of excavation by possibly using Muto Terram(requisite) (base 3) to turn the earth beneath the swamp-water into oil or a lightweight gas, have it bubble out of the way, and let the spell end once it's out of the way. This would also let you theoretically sink support structures deeper into the earth. You still need to use some Rego Terram to bring the stone from the quarry to the final location.
depending on whether you can see the bottom through the swamp water.
Actually I'm thinking the real necessity for doing magic work in a swamp is MuAq to make the water clear...
InAq 10 if you want to add duration, which you probably would. I actually hadn't thought about the MuAq option.