Making a buildable surface in a grid

We are in the final parts of making a pre-alpha release, what we are having trouble doing is creating a grid to construct on and how to go about creating it.
To explain it in the best context think Dungeon keeper 1 & 2 and Evil Genius, the ability to “mine” out an area and construct a grid. How would you go about doing something similar to this in the Unreal Engine 4?

Kind regards,

I’m interested in an answer to this one. I’d imagine you have to store the spacial coordinates of the buildable area, which can then be subdivided into the grid squares. Or by storing the center point of each grid square. But I haven’t yet tried any of this.