Hi Remmy like what Avanar & Deirdre said both are good ways to try unfortunately I would just say it's a trial and error when building roofs that look good but using planks/beams are possible the best way.
Maybe you could upload a blueprint of that building and see who can make a good job of it? and maybe that idea could even be a good thing for the Rising World community to try, someone uploads a project and then someone else adds something to it and just see what everyone comes up with.