using photoshop to make a ceiling a solid color with no shadows

I was told this can be done in photoshop. Can somone tell me how to do this or send me a link on how to do it?

Thanks,
Brent

Lasso region and flood fill?

You can render your scene with a mask (render element) where the ceiling will be a single color (for example pure white or pure red). Then you can just select that mask in Photoshop and fill it with a color.
If that’s not what you are looking for, maybe you could explain what exactly you would like to achieve. Then others may be able to help you with a specific workflow.