The “graph paper” and lines you draw in LayOut are paper space dimensions, not scaled. You’ll have to work out the appropriate real length for the line based on the scale you’ve selected.
The proper way to do your drawing is to use SketchUp. Draw at full size (1:!) and create scenes with the camera set to Parallel Projection. Use those scenes as viewports in LayOut and set their scale in the SketchUp model inspector window.