I started this UI by accident, and it's actually my first custom UI. I started a priest, and found that the amount of cooldowns, dots, and health percentages that I had to watch made my old UI really inconvenient, so over the next few days I started mashing things together in a more convenient fashion. Today I decided to make it into an actual UI with a minimal look, and this is what I came up with. The way I made it, everything except for the unit frames and buffs in the middle column can be fully customized.
Boomkin
Hunter
Priest (low level still)