Implement Landscape editor itself in game?

Hi all, I am currently making a strategy game tailored for a lab’s experiment.

I am thinking of implementing a map editor of some kind (like the ones you see in older Westwood Studio’s games like Red Alert 2 and C&C Generals)
It seems there are no such topic available as of yet so it looks like no one has yet to attempt it, although I saw a simple object online where we can already place buildings in the in-game map editor.

I am lost as to where to start with implementing landscape editing, but it looks like I should be able to find sample on placing objects in game.

That’s how you can place the buildings + even a own foilager painter:
For the custom landscape editor, you will have to take a look into the source code (unfortunately I cant help you with that :()