Hi all, little update
I've also completed the other side of the structure. It seems to have turned out quite well. Obviously the back of the plastic is completely massacred with holes etc., but so even looking through the grates you can't see the gray and above all once the primer has been applied it doesn't plug but always remains open.

Now a new problem!

Fortunately I have now learned to re-check everything, to check pieces that have came off (because unfortunately they do come off

) and then in checking what to put on the flat part (let's say the first level) I discovered that a large PE must be glued on top, and some "rails" which are in the circled part must also be added.
The problem is that these damn instructions are not complete or perhaps they are made for professional model makers, because they don't say anything about the parts to be erased. That flat piece in itself wouldn't fit on the plastic because there are several small bumps that don't make the PE stick. and
so the y must be erased. Even the 4 squares along the line of the catapult (two are covered by the red line of the circle) do not match perfectly with the holes in the PE and therefore I had to adapt them.
I honestly have to say that I find these instructions very incomplete and they make me angry every time. He could have put a series of images on the first page of what to erase piece bye piece instead of putting everything together.
Now I don't understand how these binaries should be placed: vertically on the little squares in order to create the suspended track, or horizontally with the squares facing outwards as in the instructions or I still have to fold the squares in order to have the track vertically and the squares horizontally as support.
In the 2 books I have as a reference there aren't even any tracks, so unfortunately I don't have any possible reference.
My goodness, what patience!!!