I am currently a player in a d&d 5e campaign in which we are going to use a homebrew god prestige class. My DM is homebrewing most of the gods (with stats that PCs can fight) from scratch and I was wondering if there were any rules for or guidance on converting a god, statted in 3.5e, over to 5e?
According to developer comments, gods aren't something that you can fight in 5e. They're more like forces than they are creatures. You can't fight the wind or gravity. Thus, gods don't have stats. You could fight an avatar of a god, which could have any stats you want, from an illusion that disappeares as soon as you touch it, to a commoner, or a tarasque. Killing the avatar does not actually harm the god.
This is the default assumption. If you don't like it, change it, but there are no rules so you're on your own.
There are stat blocks for Demon Lords (which are closer in magnitude to the gods. They might even compare nicely to lesser gods.) in the Out of the Abyss published adventure.