Can i make a wall out of a cube somehow transparent, while it’s collider collides with an object, like a door ?
I mean, i want to move that door, i can make holes with transparency in texture, but that is not my wanted solution.
Somewhere on that wall is a door and there this wall needs a hole.
Obviously both objects are primitive cubes.
If the door mesh is hiding the inside part of the wall you may could be using a depth mask to clip out the part of the wall mesh that is inside the door frame (this would not account for collision).
http://wiki.unity3d.com/index.php?title=DepthMask
If maybe you are interested in mesh generation and can generate the wall mesh with a hole for the door.
Clipping it out would be enough work to do. Everything should be as easy as possible and there only has to be a hole 
Hmmmm.
On the other hand, clipping it out means, that, if i open my door, the DepthMask wouldn’t do it’s work any longer correctly, because parts of the door would no longer overlap with the wall, because it was opened, huh ?