How can I set up magma workshops? They must be placed over lava or what? I don't see any documentation on this and have never messed with magma before so I am scared to even dig into it. I have a nice embark with a volcano in the west, a steep 15-z slope down to the plateau where I started and dug into, then another steep slope down to a brook.
Here's how I make magma workshops with a volcano. Dig out two large rooms, one above the other, right next to the volcano at least a few levels from the top. The lower one you will flood with magma, the upper one is where your workshops will be. If necessary aim for larger than you think you'll need cause once you flood the room it's harder, but not impossible, to expand it. Usually I go for 20x20, which gives me room for 2-3 magma smelters, 2 crucibles, a blast furnace, 2-3 magma forges and maybe a volcanic forge or armorer if I'm feeling plucky, and a few stockpiles. There are probably other furnaces but I've never bothered to build any.
The lower room you want to have a single exit point with a door. Some people use a magma-safe flood gate, but as long as the door is never opened once the room is flooded it doesn't matter what the door is made out of. It will hold. Forbid the door so dwarves and pets never go in there once it's flooded. Also, before you flood the room make sure you move out, usually by mass dumping, anything of value in there like ore you want, cause you aren't getting it later.
To flood the room, try to get it so the magma enters the lower chamber on a diagonal. That will cause the magma to flow in more slowly giving your miner plenty of time to get away almost every time. If you feel unsure if it's safe, only have a single expendable dwarf do the final break through.
In the upper room, you'll need to channel down a hole in the floor that you put the furnace over. If the furnace has an impassible square in it (the darker X's when you are placing it), then aim to put those impassible squares over the hole in the floor to make sure no one falls in, or nothing like a fire elemental swimming in the lava gets out. Unfortuantely not all buildings have impassible squares (magma crucibles for one) so sometimes you're just going to have to deal with a hole in the floor some nasty could crawl out of. It's usually pretty rare.
Hope this helps.