SOLVED: had to use wedge sloped roof for those inserts. Thanks to DevilDoughNutt on steam forums.
I had this problem in another build, I sorted it out but cant seem to get it working now. Inverted roof pieces will only point down. I’ve tried attaching them from off of roofs / walls / ceilings, next to other inverted pieces using all the mentioned combinations with no luck. The first screenshot is what I’m trying to fill in. The second is basically a mock display of what the inverted roof pieces do, just attach pointing down. The third is just a simpler build to illustrate the problem. Maybe there is a modifier key to rotate it up that I’m missing but I think I clicked through all the modes I could find.