I believe the biggest things are to make sure you lie to Othra about the lake and what to do with it. Also make sure the lizard tribe and acolytes lust is above 10, you can check their lust via the map when you hover over the ruins ( I can't recall if you need to go to the ruins first then hover the ruins location or if you can just check without having to go so just try both options).
Once you do that you can go back to the ruins during the night time I believe and fight Rhot. using reptile lures you can bring him back home. You can also bring back Roushk in this ending as well