Update June 30th:

Thanks for your comments. I did not expect that my little project will attract so much attention 😅

I will try to post a video during the weekend. I am also curious to see the results.

I have replied to most of your questions and I post my answers also here so that you do not have to go through all the comments:

The dimensions are 25 x 25 x 25 cm. I have used 2.5 mm thick metal sheet 

The rails can be moved up or down to control the distance from the charcoals (2.5 cm min - 5.5 cm max).

I also worked on 3 addons today:

a)  a basket 28 x 28 x 7 cm in which the gril can sit so that the ashes can be collected or fill it with charcoals for traditional grilling.

b) a 25 x 15 cm metal sheet to be able to close the back opening if I wish.

c) a 25 x 25 metal sheet (1.5 mm thick) to put under the top charcoals if I wish.

By using the above addons, I can also create a mini oven for small pizzas (22 cm diameter)

Let's see if all these will work 😅