What Num in Num 0/X when building mean?

Solution 1:

As IllusiveBrian communicated already in his comment, the X means in fact, how many I have on stock.

And the 0 is a counter, in my first hours of playing, I haven't encountered a construction that required more than 1 resource, but as soon I was building something that required more than 1 piece of a specific material I saw the 0 was increasing and it stated on the top line "You require 3 more of this" and when ever I selected a material the required counter decreased and the 0/X increased to 1/X where X kept being showing the overall available amount of that resource.