Ceiling Material

Those who work in a V-Ray version lower than 3.1, be careful, in the materials in the BRDF section there is Microfaset GTR (GGX). Your version is older than 3.1, then the BRDF field will be empty. Choose Blinn, Phong or Ward – whichever is preferable for you

For Corona render, it is recommended to install version no lower than 1.5, since the glossiness of the materials is adjusted taking into account PBR

Enjoy your use and successful projects =)