Ok, so I have a fort up and running in hell now. I'll start from furthest up:
The trade depot is up in the magma. I spent one hell of a time designing ramps through the adamantine, only realizing once I was almost done that semi-molten rock
can't support ramps. I totally gave up and built my trade depot up here, and when the next caravan arrived, it turned out the wagonless traders
can actually move down stairs The depot is left up here as a tribute to my failure as a human being.
This is directly below the adamantine vein, where I keep my barracks. It's on top of a house I built with rooms for all the dwarves, looking like this:
Down here is the big workshop room. I keep a large reservoir here just in case trees manage to grow and block all my water pipes. Most of the roofs/floors are microcline, while the walls are almost exclusively adamantine, since I like being awesome.
Storage room, meeting hall and hospital. The magma comes from another adamantine vein a bit north of the place. The meeting hall is packed with artifacts for maximum happy thoughts and probably worth around 10 million alone.
Below all that, actually built in a glowing pit, is food storage and housing for the people I love, which is of course militia leaders. criminals and dead dwarves.
Some furniture, more kickass rooms and the hole where stuff I hate disappear, which is of course loose stone, crappy furniture and pets.
Finally, a piece of concept art for Hell's Finest Plump Helmets, thanks to Heffa, the batshit Ukrainian I befriended just to stomp on all my parents' advice: