I have a top down view of the interior of a house. I want to put a cover on the top so light from outside can't come in and I get more realistic lighting inside but transparent so I can still see inside. No clue how to achieve this in Unity. Any help would be appreciated. Ideally I'd just be able to use Unity's built in cube to make this.
Two methods exist for this. The easier one is to just set the object's shadow casting mode to Shadows Only. I didn't know there was a Shadows Only mode and only learned of this today too, thanks to DMGregory.
The other method is more convoluted, but it can be used for other things as well. Here's the rest of my answer:
Create a custom render layer. Quote from the Layers Manual page of Unity.
The first step is to create a new layer, which we can then assign to a GameObject. To create a new layer, open the Edit menu and select Project Settings->Tags and Layers.
Put the object on top of the house, then change its render layer to the custom one.
Now, select your camera and change its rendered layers so that it doesn't render that object.
Images taken from the Layers manual page of Unity.