How to texture a realistic building?

I have made a model of a sky scraper building in unity and exported it in FBX format and imported it into unity and also I have textured it but it does not look so good and realistic like in GTA 5 and other games. How can I make it look realistic like the one below in the picture…

There’s not really a question to be answered here - there’s no magic behind making graphics look good other than being a good graphics artist.
But modern games don’t generally have a single diffuse texture - you’d expect to have a normal map, specularity map, gloss, perhaps emission map etc. Unity’s standard shader already supports all these - just plug them into the appropriate slot in the inspector.