It also sort of depends on what you're looking for in terms of 'kingdom building.' Brothel City (Patreon is under Darot Games) is more like Sim City, but with H elements. I'm also a huge fan of The Last Sovereign, by Sierra Lee, which has already been mentioned several times, but that's more of an RPG with strategy and kingdom building elements. There's also the Tower Girls RPG, but I haven't played with it enough to tell you how much actual kingdom building goes on in that one. Sierra Lee is also working on Kingdom of Deception (under Hreinn Games), which is still in its early stages, but the team working on that has already suggested there will likely be a lot of Kingdom Building going on. KoD reminds me a lot of Seeds of Chaos, which is rather more developed, and has a lot of Kingdom Building elements. Debauchery in Caelia Kingdoms (DiCK) might also be an option.