c# - Creating placement grid in Unity

I'm fairly new to C# and Unity, so I don't really know much about it.

I want to create an RTS like game where you have a huge grid that the whole world is placed on. Then you can place houses, walls etc on the tiles just like a lot other RTS games (i.e. Age of Empires, Stronghold Series etc).

How would I go about this in Unity? I could imagine having some Terrain/World manager that handles all the models and objects that you can interact with etc. And probably a lot of prefabs too with the different items, soldiers and so.

So if anyone have any smart way of doing this or maybe a link to a tutorial explaining, then the help would be greatly appreciated.