Here is a 4-plex designed for a client. He wants to showcase various features of the construction in see-through model form. Unit 1 is post-tension concrete. Unit 2 is fire-sprinklers. Unit 3 will show framing and common wall between units and unit 4 will be completed. I need some suggestions for materials or techniques to simulate an invisible wall kind of thing. here is a dropbox link to the model if anyone is interested:
Probably the simplest method, though requiring some good planning, is to break it up into key event chunks and do the transitions
in post, using simple wipes and masks. Lots of flexibility to get the timing right and dictate exactly what happens 
Hi @evan_blandford ,
The easiest way to create a semi-transparent material in V-Ray is by using a Generic material with a decreased Opacity.
To push this one step further you can add a texture to the Opacity slot.
If you add an edges map for example you can make the geometry edges more opaque than the surfaces themselves.
Another common idea is to add a Falloff texture in the Opacity slot. This way the opacity will vary depending on the viewing angle. Surfaces facing the camera can be more transparent and ones facing away more opaque.
The Edges effect can be combined with the Falloff for a more interesting look.
Here’s and example of this technique used in your model:
Another thing I tried is using a Screen-projected texture grid as Opacity map.
The benefit of using the screen-projected grid is that the opacity doesn’t stack up when you have many surfaces stacked in depth.
Something else I wanna note is that you can disable the shadow casting for the transparent material by adding Raytrace Properties and disabling the Cast Shadows option.
This approach will give you a more stylized look:
And a slightly different version:
As for the material application, I’ve used a material Override.
The transparent material is plugged in the Override slot.
The materials that I do not want to be transparent are excluded from the effect using the Can be Overridden material property.
Note that raytracing a big number of semi-transparent surfaces is not cheap and your render times will go up.
Hope that helps,
Konstantin