3D extruded shape layer – add texture or opacity to front?

Hi,

I have a shape layer, render changed to “cinema 4d”, extrude the layer in 3d space.
I can add solid colors to “front, back, side” etc. How can I either add a texture to the front (glass or something), change the material of the whole layer (like in cinema 4 itself) if that is an option in AFX (?) or at least change the opacity of the front only (not the other sides), so it would become some kind of “glass/transparent” box (but still looks 3d)?

I probably could split up into 2 layers (one just top flat surface, one 3d for behind with inverted mask of 1st) but is there another way? To keep it as simple as possible (because a lot of individual shapes).

Thanks!