Basically a two-step process once I have the box drawn: Step one is to draw two intersecting lines. Step two is to use Sketchup’s ‘move’ command in the center to pull the intersection down from what basically behaves as a single control point.
What I draft will be a little more complex but really not much harder to achieve compared to this simple example. Basically I just need a way to create new edges and control points within already-created surfaces (maybe I should be mesh modelling??). I can already do this if I create the surfaces separately and join them afterwards, but that’s a little slow.