Today I posted a picture of an Urban building that I recently sketched and painted in watercolor. I took a brief course on a site called Skillshare. (www.skillshare.com) I am not much of a sketcher but this one has me quite interested in practicing more. No perspective or rulers required here - just a pencil, liner pen and some watercolor paints. Straight lines will come with practice. It's not like your building will fall down. It's just paper so you have nothing to lose.
Let me know what you think. I am off to paint another building so hope to see you soon.