You can reproduce any details of your idea, like windows, beams, stairs, ceiling with a professional 3D modeling software.
Two Methods
Create a room model by 3D modeling software, and import it to R.Design
For detailed modeling guidances, please visit the below page.
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For imorted 3D rooms, Lumen is not supported, and therefore you cannot enjoy the best visual quality available at R.Design.
Please visit Custom Room Model Creation Request - R.Design