A little help please. :). 

I have a lizard folk who worships a old thought to be dead good. A forgotten. And I need help fleshing out ideas a bit. The god is kinda like a god of prehistoric lizard folk. Or proto element aviator/god

I'm thinking the cleric is a nature cleric.

nature cleric feels appropriate or if the class doesn't matter too much circle of land or moon druid could work or even reflavor one of the warlocks.

true, but i was asking more specificly how do i build of a god and work with a dm to make it part of the world another living part. 

There’s no mechanics or stats or rules for gods. I’d say pick a name for it, give it a couple of domains it’s clerics typically follow, maybe give it a portfolio (god of the sun, god of blacksmiths, god of nature, that kind of thing). 
I’m not sure how to advise you on how to work with your DM about it, other than to suggest you just talk to them. Some will be into it, some have very specific ideas about their world and won’t be into it. 
If, when you say living, you mean very active in the world from day to day, I think there’s ideas about that sort of thing in the new theros book. 

Here you go: SET

Flavor Set as more of a natural duality featuring death and decay, as well as life and rebirth. Set is the space between stars and is ancient even among the gods. As a cleric, focusing on the good aspects of shedding skin to find a new beginning would work, or playing neutral would allow more RP access to a necromancy and darker aspects if that is your path. Without knowing what your character wishes to embody, knowing your god is very difficult. Also, dark gods do not only have dark followers. The whims of the gods are strange indeed after all, and the idea of an infinitely old force changing its ideology, as a snake sheds its skin, would not be unheard of.