I have argued previously on this blog that divine making, like Tolkien’s account of human making, does not involve God merely “choosing” from an already given and delineated domain of possibilities so much as it involves him creatively inventing or “imagining” those possibilities in the first place. Though there are differences between his position and my own, Brian Leftow in his God and Necessity (Oxford UP, 2012) similarly argues from a combination of perfect-being theology and the “perfection” of human creativity to argue that God must be the creator and conservator of not just concrete but also abstract objects:
There are also perfect-being reasons to hold (GAO) [the claim that God creates and conserves all abstract objects outside Him]. We ourselves may cause some abstract to exist: if I breed puppies, perhaps I cause there to be new sets of puppies, new doghood tropes, even a new Aristotelian universal for a new sub-kind of dog. If we do this, being able to cause some sorts of abstracta is part of what gives us value as agents: it is good to cause a child to be healthy, and if being healthy consists in bearing a health-trope, it is good precisely to be able to cause this trope to exist. It would be a defect in God if He could not manage what we ourselves can manage and there were no explanation of this from some other divine perfection (as, for example, we appeal to God’s character to explain the fact that though we manage to do wrong, He cannot). Perfect-being theology denies that God has defects, and it does not seem that some other perfection would explain an inability to cause new tropes to exist…. God’s perfection in this respect may consist partly in ability to do a great deal more of it than we can… If (GAO) is true, God has power over the existence of the abstract as well as the concrete, including anything necessary and abstract. (65)
In summary, if it is a sub-creative perfection that we are able to invent “new form” (as Tolkien puts it in “On Fairy-Stories”), and if God is the perfect-being, possessing all perfections in an eminent and infinite manner, then God must be a perfect (sub)Creator.