You can download the demo project here (4.21) : https://drive.google.com/file/d/1kho5onMj6mUZwjgBJmvtNzRlm4sluqws/view?usp=sharing
The demo project shows you how to setup this tool to create either Dungeons or side scroller levels.
The folder hierarchy is the following :
Inside the Blueprint/ folder, the structs and data tables are used to store dungeon parts to spawn. Those elements are used by the two BuildingLogics (BuildingLogic_Dungeon and BuildingLogic_Platformer) to spawn the dungeon parts in the painted cells.
The InstanceActor is just an actor which inherit from DungeonInstanceActor. Put it in the level to define a new dungeon that you can select and paint on.
Utilities is a MacroLibraby which gathers several utility functions to place items inside the dungeon. Those functions are used by the two Building logics.