Hey Juan, I'll be handling the critique for your 250 box challenge, but first of all let me congratulate upon completing it as it certainly requires time and patience.

-So let's start by addressing your linework, your additional lines tend to come out very messy there were a number of factors that didn't help you, but I think the most important is space, you had a tendency to draw relatively small boxes, and keep in mind that this makes it harder to ghost through your lines and to draw from the shoulder.

-When adding lineweight keep in mind that you want to ghost through each superimposed lines and to add only one, as we want to keep it as subtle as we can.

-There were numerous cases where you added lineweight to the internal edges of your boxes, the initial lines that form your Y shape for example, you only want to add lineweight to the lines that represent the silhouette of the box.

-As a final note regarding your linework, keep in mind that you also want to ghost through your hatching lines, they have to be as smooth as possible because they're sitting on top of a completely flat surface.

Now let's address the boxes construction.

-You had a tendency to extend your lines in the wrong direction, take a look at this diagram, ultimately what you want to keep in mind, is that you should extend your lines starting from the initial Y and extend them towards the direction they are pointing to. If you see a set of parallel lines that are diverging, it is very likely that you have extended your lines in the wrong direction

-Keep an eye for diverging lines, as shown here.

The key things we want to remember from this exercise are that our lines should always converge as a set not in pairs, never diverge from the vanishing point and due to perspective they won't be completely parallel.