how to make the colour of the roof uniform

Frequency separation is also an option. 

https://community.adobe.com/t5/photoshop/how-to-even-out-different-colours/td-p/10922039?page=1

Edit: 

First, put a steep Curves layer on top to exaggerate the difference and you can better see what you're doing. This is just temporary; delete it afterwards!

Then put another Curves (or Levels) layer under it. Set it to fully adjust the most affected area, and then some for good measure. Invert the white mask so that the adjustment is fully hidden.

Now, the trick is to use a large soft brush to paint in the adjustment with white. Keep it at low opacity so that you can gradually build up until it looks good.