I highly recommend downloading the Vaper's Toolbox app. Too much experimentation with a total lack experience or understanding of how electricity works is a recipe for disaster. KNOW how electricity works, how ohms affect current and draw, and what your battery is capable of. Otherwise you could end up with a face full of acid. I'm not saying don't play, just know the rules before you joining the game, if you know what I mean.
But to answer your question; Try building 2 coils using a 7/64 drill bit. Build the coils at 6 warps each, that should get you very close to .4 ohms. That build will give you a general idea of a safe build that produces big vapor.