You may ask yourself, "What is that beautiful house?"
You may ask yourself, "Where does that highway go to?"
And you may ask yourself, "Am I right, am I wrong?"
And you may say to yourself, "My God, what have I done?"

From here I usually clarify details with cleaner linework on a separate layer; If I'm feeling frisky I might also create a guide layer to figure out perspective and stuff. Usually, I just jump right in and lock it down, so I can move on to the next idea buzzing around in my brain. Gotta love ADHD.

Add some finer details with a Sharpie pen, spritz some Dullcote over the top, and you're good to go.

I've found a quick way to give a weathered look is to lay down base colors with acrylic paint markers, add some shading with water-based markers, and then blend it with a light-colored alcohol-based marker, which gives a grimy, aged quality to everything.