Creating lines on top of image

Hi I have drawn a stage, but I would like to add lines on top of the drawing in another color. So I thought I create a layer.
But when I do that, the original lines from the layer above will disappear. What should be a good sollution?

The is with the blue line

Now the line in the first layer is gone

Share the SketchUp file so we can see what you’ve got going on. Are you trying to represent grout lines or something?

No I am trying to find out what is the best efficient way to build frames below the decks?
This is a stage.
I am now doing it by hand with a pencil and paper

But I found a way to do it with the drawing from the client and foxit pdf.

You’re using SketchUp. Make a 3D model of the stage. That’ll be better and more accurate that trying to use single lines to represent the frames.

Your profile indicates you are using Sketchup 2017 Make. You are not permitted to do commercial work for clients with that version. You need to be using SketchUp Pro or SketchUp Go.