So, I bought new tool for pop rivets (that is how we call them, expanding rivets maybe in english?), that did allow me to easily attach new roof 'spoiler', it is bit short I think, but that is because I really would like to get transparent one, so that I could make angle to decrease bit more for last 50%.
Here is first 50% in poor photo:
It is plywood, I had it around and it is easy to work with, when painted it is not too bad, I just need to use bit filler to make it so that there is not sudden 'step' where it starts.
Maybe such roof extension does some good?
I also did see that car has roof and side separated by small edge, so I thought that I maintain that edge in my roof extension spoiler thing, also putting edges to same position would of cause quite lot of stress to parts.
Top part is curved same as roof, it comes down slightly steeper angle than roofline, next 50% made from clear plastic, I plan to make so that it comes down bit steeper.
Now maybe I should make last inch of clear plastic to go horizontal level so that it promotes separation of airflow? It should be possible with heatgun to make such form.