What is the best way to add an arched soffit over a window and a soffit for a light in the ceiling.
You are not offering a "Tip or Technique", you are asking for help with your project.
This question belongs in the "Q&A" forum category.
Arched soffit: Extra thick wall with an arched doorway.
Ceiling soffit for a light: Divider wall "room" with added ceiling height.