Mapping Grid/Tile Systems

Hello everyone.

I have a questions, but first let me explain about what I am trying to do before I get right into the question. I would like to make a "build your own dungeon" style game, similar to what can be found in Dungeon Keeper. To do this, I would like to use a grid system which would allow me to set different textures, or a unique mesh in the select spot, in both the terrain editor, as well as in game for the players. (Similar to a Minecraft effect)

Now that I have the basis of what I would like to do out of the way, my questions is: What are some of the best ways to go about this? I have actually looked at the ones in the asset store, but i'm not sure most of them would work for what I want, so if anyone has any first hand experience with the grid assets, and know how they function, and work, I would appreciate any suggestions.

I am new to using Unity, so I am still trying to figure things out. (Not trying to take the easy way out, just wondering how people have gone about this, and what assets would work)