To do that you will need to use the Magic cube tool. Check that video tutorial for more info:
Below you can also find written instructions.
Create floor trim and decorative wall moldings
You can use Magic Cubes to add custom skirting boards, wall trim, or decorative rectangular panels.
For more detailed molding profiles, you can also explore the ready-made objects in the Planner 5D catalog.
Create floor trim
Add a Magic Cube to your project.
Resize it into a long, thin rectangular strip.
Adjust its length to match the wall where you want to place it.
Position it along the bottom of the wall.
Apply your preferred material or color.
For example, a simple skirting board could have the following dimensions:
Width: 300 cm
Depth: 2 cm
Height: 10 cm
Once your first strip is ready, duplicate it and place copies along the remaining walls.
You can adjust the length of each copy to fit different wall sections.
Tip: Remember to leave openings for doors and check the corners in 3D to make sure the trim pieces connect neatly.
Create decorative wall panels
You can use the same technique to create rectangular wall moldings.
Create a thin Magic Cube and position it vertically against the wall.
Duplicate it and place the copy on the opposite side of your planned panel.
Create two additional strips and rotate them horizontally.
Position these at the top and bottom to complete the rectangle.
Apply the same material or color to all four pieces.
Once you've finished your first panel, you can duplicate the individual pieces and move them together to create matching panels across the wall.
To select several pieces at once, hold Cmd (Mac) or Ctrl (Windows) while clicking each piece. Duplicate the selection together to preserve their positions relative to one another.
Tip: You can also search the catalog for decorative moldings, skirting, or wall panels if you prefer to use ready-made objects.