One of my players wants to use a Demon he intends to summon to build him a Manse.
Looking at the rules this seems to be within the scope of a demon contract. Core Rule Book p.473
Alternatively, she may assign it to complete a specific task—“Construct a tower using these plans,” “Murder Magistrate Yang,” “Dig a tunnel through this wall”—for as long as it takes to complete. Task-bound demons form a Defining Principle of “I must complete my task,” which is similarly impervious to tampering.
The core of the question I have is how can this be handled? But that question could be broken into a few subparts. Are there any rules that would apply to this situation, and what are they? Also looking for practical experience of how this has been handled by others, and how to avoid the player being able to build castle after castle just using demons as "free" labour. Prefer the suggestions of how to handle it to be linked to rules for 3rd edition.
It would be a bonus if the answer would adress if this would be different if the player "only" wanted to build a mundane tower.