I can't get walls on my building

HELP
Hello i am working on this building and i want it to have walls. As far as i know a wall should be created when any number of lines are connected. All of the lines are connected at my buildning but there are no walls. The walls should be between all the arches.
Can anyone help me?

Use the Line tool and stitch the vertices on the arcs together to create faces. You should only need to work up one side, though. Then you could select those faces and use Rotate/Copy to make the other sides.

What you are missing is that in SketchUp curves are approximated by collections of short straight edges and curved surfaces are approximated by collections of flat (planar) faces. You can create the illusion of smooth curves by softening and smoothing the edges between the faces.

So, it is not enough that the lines are connected side to side, they also have to be connected up and down to create all those flat faces. As @DaveR wrote, you need to add the up and down edges that create all those flat faces - this technique is called “stitching”.

In fact, you may only need do one half of one side and then copy and flip it to create a full side. But for that to work, you would have to have vertices lining up along the centreline.

You need to understand the structure of SU geometry, it is made up of edges and faces that form when the edges are coplanar. Coplanar really just means that they align to form a flat face. 3 edges will form a face but four or more may not, so you need to build your geometry in such a way that faces can form, then you can soften the edges between those faces to create curved surfaces.

In this gif I have shown you how stitching works, as mentioned above. Note how I join endpoints and how the flat curve will form as four sided faces but the more curved area needs to be triangles. Also note how you can miss an endpoint. I have used ctrl with the eraser tool to soften the edges.
Stitch

Thank you all so much! It was a huge help. I just didnt knew that curves were made up of multiple lines. But now it all makes sence :wink: