How do I subtract excess material from overlapped walls?

I have an unconventionally shaped floorplan/building I’m constructing, but all the intersecting walls are giving me real issues. I imported a dwg file from AutoCAD, and was working off of this floorplan to build up and guide my model. The floorplan is a triangle and the roof is weirdly shaped and slowly slopes down, so there are a lot of complex shapes going on. I want to work off of the pushed up floorplan walls, and slowly carve away at them until I get the structural shape that I want.

Basically, because the building is an odd shape, I keep having very ugly walls that overlap and intersect. I have tried to use the subtract tool to get rid of the overlap, and it didn’t work. It keeps saying that they “aren’t any solid objects to select” even though they are. I also tried using the push/pull tool to subtract out the overspilled walls yet it still wouldn’t work. I also tried using the “intersect” shapes tool and it did nothing.

Has anyone made a tutorial on how to solve this? I feel like I’m going crazy. I’ve spent all day researching and working on this and it has got me nowhere.

Do you know if those walls are raw geometry, groups, components?

Basics of SketchUp at

If you can, post your SU model here.

If you can include the dwg files inside the model, that may hekp.