If I understand you correctly, the question you are asking is "How can I do a sun study of the floor plan, but with the roof still in position so you can see the shadows cast from it?"
Palawat gives a possible solution
here.
To paraphrase - Set up a new lightworks material with the material's Colour Class set to Plain > pure black and set the Transparency Class to Plain > pure black also. Temporarily apply this material to the roof and any other structures you need to see through but still want to cast shadows.
Apparently there are some issues with multiple light sources, but give it a go anyway!
What's really needed is a true 'shadowcaster' material/shader. One that's completely transparent, yet still casts a solid shadow.
I wonder if Artlantis has this function? Dwight?
Hope that helps!
