Then how do you explain the fact that every society in human civilization has created some sort of god mythology? I don't think it is a stretch to admit that there is some sort of built-in trait that makes us expect there to be something greater than us.
In female-centric societies, the gods were females--or at least the most revered gods were females--and in male-centric societies, the gods (or God) are male. It's very easy to see that we have created gods over and over again in our cultures, and those gods directly reflect the very nature of our culture.
My best guess is that we create Gods because we are an inquisitive species. We want answers to everything, we are knowledge-seekers. And when we are encountered with something we just can't wrap our minds around, we are not satisfied with no answer. "I don't know" doesn't cut it. So, we create a deity. I forget if it was Einstein or Hubble that said, after getting an understand for just how vast the universe must be, said that the more he discovered, the more he believed there must have been a creator.
That right there tells us when and why gods are created. Our last frontier as a species is, obviously, space, and because looking into it is akin to experiencing an earthquake 10000 years ago, of course we're going to see it and say "Yeah, there's no way this happened without some help."
If you want to make a logical argument for the existence of a god, then point to the fact that we, as a species, tend to believe. Don't point to a holy book, don't point to any specific religion's lasting power, don't try to put a face (or a number) on this supposed being. If there is one, none of us know who it is, or how many of them there are.
. Accepted, it became our ancestors legacy. Therfore, Gods had been heard of before. It wasn't like every civilization suddenly dreamed them up. God was passed down like a handshake.