I dont currently have one... I can probably convert my current "green glass megaproject" fortress into a demo unit though, but it will take a considerable amount of time. Especially since the entire fortress is above ground, and made of constructed materials, allowing me to rebuild whole areas to suit the new purpose. Invaders are currently off, because this is not intended to be an actual play fortress, but is instead an experiment in building infrastructure, abandoning, and then embarking over the top again with JustEmbark!. It's kind of a science project, but only informally so.
The trick, is in constructing an automated pickup and delivery system to get raw materials in (including dwarves!), and finished goods (including children!) out. Roller powered minecarts with fill quota requirements on isolated tracks looks like a promising solution. Goods fall directly on top of the minecart, and-or, the isolated minecart systems are also secondary work-center pods, with full-time operation staff. Not sure how to manage that.
Inside each pod, are all the amenities and requirements for dwarven living. These include a farm plot, a still, several overflow stone pots, a farmers workshop and clothing chain, bedrooms, an actual intended use workcenter, and a well decorated dining hall. Essentially, a mini-fortress, designed for 3 or 4 dwarves. Seed overflow/destruction becomes a necessity to keep these systems operational. Dwarves can theoretically live inside their pod forever. All dwarves have farming, clothes making, spinning, plant processing, and brewing labors enabled, and orders are given as needed. This ensures that pod residents are never naked, nor go hungry or thirsty in the event that the distribution system fails.
All entry in and out of the pod occurs using a 1z drop zone, using a retracting bridge over the "input" side of the pod, and another such retracting bridge inside the pod, over the top of the distribution "output" chute. Dwarves are dropped in and out using special burrow designations that have them stand on the bridge. All levers to activate these bridges are inside the pod, after final comissioning. (This is tricky. You cant make the pod impenetrable from the start, because the mechanic that sets the bridges and levers up has to be able to walk upstairs to the bridge to link them. This means that the pods need to have at least 1 constructed wall to block up the pathing hole, and need at least 1 dwarf inside to further commission them. After trapping Urist in there, he is then the lever operator, and can safely operate the dropchutes to get dwarves in and out.) The levers to things like the "Flood the fortress with magma!" subsystem are installed in these isolated pods, so that even with a SEVERE contamination of the green skinned menace, a full fortress decon is possible, without risking dwarves being in the hallway (since they are all in pods, except for the broker, and the loading/unloading crew for the trade depot, who are themselves just an isolated pod with a unique function.). Just be sure to use magma-safe bridges for the dropchute covers. Bridges are indestructible to building destroyers, making them the preferred system-- further, they dont get compromised by vermin like kobolds, who render doors and hatches unlockable until reclaimed.
Handling more than a dozen pods will quickly become impossible to manage though. That means each pod should ideally have at most 16 dwarves inside, and should be designed to be able to accommodate this number. (That will give you a max pop of ~200.) Residents of a pod will never encounter residents of other pods ever again after being installed, unless they are children being micromanged into a new pod to fill a vacancy, and or to maximize/control genetic expression. (Dwarves need to be unrelated to pair up, and cant be more than 10 years apart on age.) Losing a single pod should ideally not result in any adverse thoughts of any other pod's members, because they are isolated communities. children should be removed from their mothers as soon as they start walking on their own, to avoid inter-pod friendships and relations. Completely unwanted children can be isolated, and terminated.
A "Special" meeting hall that nobody uses, is used to process migrants for integration.
I think I can get this all set up over 4 Z levels. (top level contains a perimeter wall surrounding windmills to power the minecart network, next level down contains the "Fortress main level" which has the migrant processing hall, and all the dropchute activity zones, next level down contains the isolation pods, and the layer below that contains the distribution tracks to return goods to level 2. Level 1 and level 4 are connected by one multi-stacked section of vertical axles from the wind farm above, to supply power to the minecart network.
The greenglass megaproject embark I can use for this is conveniently on top of a volcano, near an ocean, with an aquifer, making all necessary resources copiously abundant. (I can *manufacture* obsidian for all the magmasafe stone mechanisms I need, and the magma is conveniently close to the surface, and easy to direct and place.)
I might just do this.