Assuming that a supreme creator exists and that he created the entire universe then we’re in the wild west since science only deals with known things and this divine spiritual can’t be measured or examined.
That makes all answers to this question would be pure speculation to make it fit into our understanding of the world as we know it and resulting in a big “we don’t know”.
Assuming he/she is made of atoms and given we haven’t seen it on earth we can more or less determine that it’s either smaller than a human or not on the earth or in the atmosphere. It can also exist in another reality that can’t be seen or measured from ours deep inside the earth or ocean.
To actually get anywhere with this question you’ll have to make a lot assumptions until almost all the assumptions become the answer.
In Christianity God is Jesus and Jesus was made of atoms. Thus God did exist and was made of atoms at one point at least.