I don't know how you structure your builds yet, as I've only been a Patreon supporter for about a month now, give or take. But assuming you don't work on giving every character content in each build, or if you give some more than others, maybe you can run Patreon-exclusive polls to see who people would like to see more content for? Not saying you need to run polls specifically on that, but something that would give people a voice could draw people to your Patreon.
But honestly, the work and quality you put into this alone is the biggest reason people would want to support the project. It's evident to see, and there's not a whole lot more you can do than that besides a few little extra things like polls.