This did not come to his mind up to now. And maybe he will not get aware of that up to the moment he can´t ignore it anymore.
First he will try to get permission to dig out an underground cave maybe with a long floor to the cliffs creating windows at the cliff side. Secound and even more complicated due to his weakness in terram he must find a way to construct this cave and find a solution for the window.Very time consuming, but with a longevity ritual…
Doubtful that he would not have considered this. But as soon as he realizes the problem, why would he remain at a covenant that has fairly stiff limits on available space where he can grow for his artform?
There were some negociations between the original magi and the villagers living on the plateau, and one of the constraints placed on the covenant was that they are not supposed to excavate into the cliffs. That clause was not popular with the magi, for they hoped to do pretty much what you describe, but it is still there. Breaking that clause would certainly cause ill will with the villagers, should they learn of it. And so far they seem to have a knack for finding out what the magi want to do...
Which is why I am bringing this up before you develop the character too much. Considering that he is weak in Terram (and none of the other magi are very strong there either), why go to all that trouble when it would be far simpler for him to try and find an existing cavern somewhere on the continent, instead of trying to dig up one on the island? This doesn't seem well-suited to the covenant so far.
He will try to increase his Profession Ice Sculpture before he is Satisfied with the results. Many of his creations will not satisfy him. Maybe he will melt them and restart the work or if he is in a bad mood smash them to the wall. So the first room will not be filled up too soon.
Sooner or later he might start to plan an underground art gallery and invite some guests that are interested in his work. But before he can do this he will have to find a place that will provide the resources needed for this. He is willing to work to get these resources. And maybe a young covenant has a need for his gentle gift? Sometimes he has to deal with the mundane. And if he do this well that is good for the covenant. What is good for the covenant is also good for Torros and his resources and his position within the covenant.
It´s not just finding a cave! He will need a community, an income, a shelter (beside the cave), vis and some adventure to keep the creative energy flowing.
(I (The Palyer) know he will never get permission for this excavation. But the Character didn´t know, and don´t want to think about it)
That's what I wanted to make sure of. I don't have a problem with the character being unable to fulfill his goals, so long as the player has fun with it. Didn't want you to become irritated at the obstacles your magus will face.
Although it will also make you work hard at finding reasons why he will remain there.
Perhaps your magus is simply lazy and doesn't want to start over somewhere else? After all, if he dropped his initial plan, perhaps he is simply someone who doesn't have the drive to complete his projects. Just a thought.
That sounds good!
I thought to give him some extravagant touch (like an artist).
Why not a lazy artist that sometimes just waits for new inspiration.
A person with an erratic mood: Sometimes charming helpful and cooperative, and sometimes uptight and touchy.
I was one of those expressing an interest in excavating the rock beneath the tree and the location of the covenant and to be honest I (or Japik) hasn't completely ditched that idea. Now with some ranks in Terram he could see himself doing part of the job but it probably needs a lot of time, first to increase Terram and Perdo further.
An OOC question to you Arthur - if you want to answer it - will you allow excavation from a GM standpoint? I understand that we could get in trouble with the villagers and that is one thing we need to address in-game of course should we get there but I would like to know if you say that it's completely out of question to develop the covenant in such a way as excavating the rock. If it is possible then Japik would probably encourage your character Flavius that he will get an excavated grotto for his ice sculptures eventually. Of course to Japik everything is possible even if it isn't always. 
Maybe you or someone else can create a Magic Pickax that helps to carve out some caves.
Arthur, would it be Ok if I submit the character draft next Sunday?
If needed, I can do it faster.
No problem for me. The character will only be introduced to the covenant after a little introductory period played on the side, much like I did with Joel's magus.
That will help you realize what his capabilities are and gauge the way I handle things. It also helps me learn what is of interest to the character, and the kind of stories I can spark for him. So don't expect your magus to interact with the others right away.
Character's stats moved to its own topic.