Knight,
Others may do better than me, but I think that it would be easier for people to suggest things if you explained what is wrong with the picture (what are you trying to do that is not there) and posted the SketchUp file in this thread. Even if we see where you are not getting what you want, the particulars of the model cannot be understood by pictures alone.
If these "layers" are groups, pushpull will only work inside a group. It won't affect other groups.
Pushpull comes to "constraints" as it moves into secondary faces, where faces are not square, or some geometry connected to the P-P face would be impossible (illogical) were the face to move further. If I were puzzling over such a thing I might turn on "color by axis" in Styles ( Style window: "Edit, Edges tab, Color: by axis") to see how my object edges are aligned (assuming they are related to the model axes at all).
Also are you modeling in parallel projection? I find perspective view is easier to work in, in most cases. Parallel has particular uses, mostly for the orthogonal views.
Please try posting the file.
Good luck. Peter