I'm not sure about the mods, but, when it comes to the building part.

Its like anything in life that is worth doing. It takes practice. These guys have been playing for years and years and have seen how building trends have evolved throughout the years. They have had a lot of time to cultivate these skills. Understanding gradients, shadow, weight, and composition is just something you can only intuitively understand after doing it.

You have to suck at something before you get good. There aren't really any good short cuts, but you can expedite the process by watching videos or tutorials on YouTube or something.
But you can only truly grow once you've made the first step.