Horrible looking baked lighting (jagged, very dark/bright)

Hi,
I need to improve a project made by other people in 2015/16, which was about creating a virtual representation of our school. However, I know only very little about Unity development. The building itself is made up of just two meshes:

the entire thing is in one .dae file.

One of the meshes has 36 different materials and I have no idea how that works but it does:


With realtime global illumination it looks bad:

and my job is making it look better, so I thought, baking some higher quality lighting should improve it:



yea, I have no idea what's going on, Unity is yelling at me telling me there's 6000+ overlapping UVs however I don't know if that's the problem or not. Could someone please just give me some resources or something to give me a chance to fix this?
These are my lighting settings btw:


I'd really appreciate it if someone could point me in the right direction, I'm lost.

 

Send me your model to show you how to setup its lighting step by step

 

Here it is! Thank you

 

Where is the textures?

 

Sorry, I forgot the asset uses external materials. Here they are. You can see the order in the screenshot above

 

Your model is not suitable for game engines
1. Your model is too big... you must separate into separated models
2. Your model is combined... must be separated parts

For large models/scenes you must import models separately and place manually in the scene inside unity
I imported your model into Maya LT and it crashed

Sketchup notes:
1.When you are creating a model in the Sketchup, you must know the back face culling article.
2.Your model problem was that has been exported using two sided face mode(select/change from export window on Sketchup). This is not usable for game engines

 

Thank you very much for the explanation!! Unfortunately, I did not make or export the model and do not have SketchUp available, but I'll try to find a way to implement your suggestions.

 

How much smaller do the separated models have to be?

 

For example:
a house :
Chair is 1 piece
Each sofa is 1 piece
Each room or wall is 1 piece
Each roof light is 1 piece
Each door is 1 piece
The clock on the wall is 1 piece

On the other word, each set should be a piece

 

Thank you very much!