Alex

The new game involves the mechanisms of both RPGs and Sity-buildind. Where can be built a building, a wall, a tree, improving their level and so on
Including the destruction of the building and any other buildings. Can this be realized?

UserName

Well I think your could make your buildings as combatants, and to build them you use a value input dialogue node to ask the player for different options. So essentially buildings are non moving combatants with stats, and to level them up you can use the same experience system that's already there.

gamingislove

It'd involve heavy use of the event system with game variables and prefabs. You'd basically have to store the type and position of each placed thing in variables (e.g. type as a string, like 'house' or 'tree', the position as a Vector3).

It's doable, but not that easy - I don't know if there's an asset out there that allows doing this, but if there is, it's probably better suited for this task :)