Hi Alessandro,
In this case I'd probably break the window into smaller components, one for the glass and a single side:
You can then use the side segment to create the start and end , using a mirror operator to create the other side. For the corners and evenly segments you can combine the side and a mirrored version together to create the joins between two windows:
The advantage of this is that you can make the windows any length without deforming the width of the side of the frames.
The final step is to create the divisions. Using another composer operator to combine two side segments, you can then use the Evenly input to divide the window. You can easily duplicate the generator and use different material IDs if you need to adjust evenly distances in other locations.
Please find attached an example using this technique.
I hope that helps, please let me know if you have further questions.
Cheers,
Paul