Let's be honest

[Mister Agenda]

Not sure how you get to the claim that a matter creating god is necessarily immaterial.

The idea is that before God created matter, there was no matter.

If God was made of matter, then there was already matter. 

So the thing that created matter couldn't be made of matter.

Or, before God created existence there was no existence, therefore God didn't exist to create existence. You overcome this by restating it as 'before God created existence, nothing but God existed'. You could easily go the same way with matter: Before God created matter, God was the only material thing.

Apologies and credit to HappySkeptic, who ninja'd me on this point.