Well - BSP is definitely something from the past so you will need to learn either 3ds max or another software like Blender (which is free).
You can import CAD data into max and then just build your walls based on that CAD data. Then it will be precise. 3ds max has lots of tools that help you to be precise. It’s not that difficult once you know the basics. But yeah - 3ds max, despite probably 10 redesigns of the interface is one of the most confusing applications ever made.