How to fill between two solid groups rotated from each other?

Hello everyone. New to Sketchup Make 2017 and love the ability to take my thoughts and put them into a model. I am building a Town Square (see pic - I can only load one image since I am new) that I need to be able to 3d print when I am done. I have created my solid groups of my buildings and you will see that some are rotated from the others ~25 degrees to create the curve at the ends of the square. I want to continue the back walls and roof lines to intersect midway between the two groups to fill the gap between the rear of the buildings. If you were to actually build this out of wood, you would just continue the back walls and roof lines over. However, everything I try in Sketchup causes an object that is not solid (not printable) or has lost lines inside the structure. I know there must be a simply way to do this, and I just do not have the experience to know. I have searched the forum and did not find anything specifically on this topic (unless my key words were incorrect) Any ideas how to do this? Remember I am new, so details in the explanation would be appreciated.

use the tape tool to extend the lines and use the intersections for inference to draw new wedge section?

or this way

Thank you for the lesson. That worked perfectly after a little practice.