Use this to get you started:

omg! lots of groupings... i need to understand your solution properly before I make it for the whole house. Thank you very much for the push ... i was also trying another way of getting this done by creating a shape... like how you suggested earlier. Will try both.

I'm sure Kevin can create a much better corner with Blender like he did with the roof tile but it's a weird shape so this is what I could do with the Sweethome3D Create Shape tool.

what you made is close to the actual shape... wondering what is the mathematics behind calculating the coordinates. If Kevin can make one, it would be better.

Thanks both of you for helping me.