How to find right values for zoom and tileSize variables

[shuoros]

I wonder how can I find out the zoom level of the picture that I get from google map to set this two variables to work properly on my images?

Here is a sample of image that I want to detect the rooftop potential for solar panels:

And this is the output:

As you can see the result is not good at all and the predicted area of room is also totally wrong.

I think the problem is the wrong values of zoom and tileSize variables.