I have started using the cool White Model Effect setting to quickly render some interior scenes. 
As you can see from the image, i am facing some issues, mainly the evident patchy surfaces (and not nice and clean) 
Can someone please put me on the right way to get better at this? 
I believe it has something to do with the light/shadow setting, but i wouldn't know. Basically, being an interior scene, i need lights. What I did, i put the window light object on every window, as well as assigning the Glass Light material to actual lamps (you can see they are lit up) but apparently it's not enough. Any other hidden settings i should be aware of? 
I also attach the render settings. 

Any help will be apprecited.
I didn't find the right solution from the Internet.

Creative video advertising studio

Thank you