In Berkeley’s system there are two kinds of entity: ideas and spirits (finite and infinite). What we call “material objects” are not material at all but ideas in minds, our own and God’s. There are no material entities, only ideas and immaterial spirits. God is the basis of all reality and objects only exist as ideas in his mind. At the other extreme, we have a view like that of Hobbes: all entities are material, including human minds and even God. And then there are the dualist views that postulate two sorts of entity, material and immaterial, with ordinary objects as material and minds (human and divine) as immaterial. But one position in logical space does not appear to have been occupied or even contemplated: the position that ordinary (“material”) objects are ideas in minds, ultimately God’s mind, but that minds themselves, including God’s, are material. That is, tables, chairs, mountains, and atoms are “ideal” entities, having no existence outside of minds; but minds are material non-ideal entities—and that includes the mind of God. God is made of matter while so-called material objects are made of mind—they are merely ideas that exist in minds. Thus the objects of perception are all ideal, but the perceiving thing itself is material. Instead of the traditional theological position that God the creator is immaterial while his creation is material, we have the opposite position—that God is material and his creation is immaterial. The universe is immaterial but God its creator is material.
This position does not seem incoherent; it simply adds materialism about spirits to Berkeley’s general theory. If finite spirits can be material—this is at least a logical option—why can’t the infinite spirit be material too? Why can’t God be made of matter? What is to rule this possibility out? Not God’s supposed infinity: why can’t there be an infinite material substance with infinitely many attributes? It is no more difficult to be infinite if you are material than if you are immaterial. Suppose we define matter as extension-in-motion: then God will consist of an infinite number of extended things engaging in infinite amounts of motion. Or at least he will consist in as much extension-in-motion as is necessary to account for his mighty powers. Only, it seems, a general hostility to grounding mind in matter could stand in the way of regarding God as made of matter (supervenient on matter, etc).  If materialism in some form is coherent for finite minds, why is it not coherent for the infinite mind (whatever exactly this infinity comes to)? Couldn’t the Greek gods be material? Weren’t they?
Is there any reason to look with favor on this inverted form of metaphysical dualism? There is if you are puzzled about how a mind could exist without any material support. If you find it hard to accept that finite minds (human and animal) could exist without a foundation in bodies, why is it easy to accept that God’s mind could exist without such support? If minds are necessarily ontologically dependent on matter, then the same dependence applies in the case of God’s mind (or the minds of gods). In order for God to have ideas in mind he needs a substrate of matter to keep the whole set-up going—he needs something material for his mind to supervene on. One argument for that position is that in order for his mind to be dynamically active it needs a foundation in motion, since only motion can ground change over time. How can God be the cause of motion if he is not material? Anyone who is suspicious of the notion of self-subsistent mentality will jib at the idea that God’s mind lacks any material being. Objects don’t need matter to sustain their being, since they can be identified with ideas, ala Berkeley; but spirits are not ideas and hence call for another form of sustenance—either as self-subsistent immaterial substances or as products of an underlying material substance. The former view is problematic but the latter appears perfectly coherent. Of course, God did not create matter on this view, since he requires matter in order to exist at all: but he didn’t create himself either according to traditional theology. God depends for his existence on matter, but matter is capable of conferring the powers that he needs (as the material universe before the big bang had the power to create the universe after the big bang).  So there is no logical obstacle to identifying God with a material substance, so long as we are generous about the extent and powers of matter. And there is nothing to stop us positing non-trivial emergence with respect to the matter that composes God—he need not be reducible to matter.
Thus there is a metaphysical position here that has not been recognized: materialist idealism. The world of perceived objects consists wholly of ideas in minds, but minds themselves have a material nature—up to and including the mind of God. God is a material thing but his creation is not material (except for the finite minds he has created). Everything is purely mental except minds.
 Isn’t it a limitation on God to declare that he has no material attributes? Then his creation would be ontologically richer than he is (in one respect). And is it that he can’t have material attributes as a matter of necessity? But then his omnipotence is limited. Nor do we have to suppose that the substance of God is somehow humdrum if he is made of matter; matter could be a lot more exciting and mysterious than we suppose from our limited perspective.