The Escapists 2 has a free prison map editor

Prison escape 'em up sequel The Escapists 2 launched back in August, and has since served fans outer space cellblocks, transport lockups, and themed DLC. Now, a new update lets players build their own correctional facilities. 

The game's Prison Map Editor has players dragging and dropping a host of rooms, equipment, cells and more as they craft their ideal jailscapes—with optional multi-floors and, crucially, ventilation space wedged between them.

Here's a trailer:

Most interestingly, finished facilities can be shared through the game's Steam Workshop where you can sample a host of other budding architects' designs in solo mode, or local and online multiplayer.

The latest update also targets a number of bug fixes—the sum of which can be found in this direction