Measure the area on the walls that will be occupied by the panels. Use a yardstick to trace the outline with a pencil.
Cut the trim to fit. Measure the length for each part of the trim and cut it to fit with a circular saw. Make a 45-degree cut on each end by tracing it out with a pencil and feeding it through the saw. Do not push the wood through the saw — glide it gently. Always use the blade guide and keep your fingers away from the blade.
Finish the trim. If you will be painting the trim, sand it lightly with a fine-grade of sandpaper. Prime it with an interior water-based primer. Let it dry for at least four hours and then paint it the color of your choice. If you choose to stain the wood, sand the wood and apply a coat of wood stain. Let this dry and sand it lightly before covering it with a clear coat of polyurethane.
Attach the trim. Use color-matched nails to nail the trim to the wall. Use a level to make sure each piece is perfectly level before you nail it in.
Finish off the interior of the panel. For an interesting look, paint the interior with a contrasting shade from your wall paint or install wallpaper inside the trim. You can also leave it plain if you prefer.