Trying to make a fallout shelter type game.

After Reading some other members questions and reading guide line I am redoing this question lol

For info first: I want to build a game similar to fallout shelter as in building on a 2d plane above and below the ground line. Want similar game play as in assigning npc's tp different jobs. I wish to include some tycoon aspects and simulation also. resources and sim's style where need keep your npc's happy.

I want to include vehicles and capturing other "vaults" as well as more combat. My current hold up is creating a grid where people can dig and then build a room. I have check other peoples question and none have been answered in way i can use personally. What i need is a grid 10wx10h below ground and 10wx5h above ground. So since supposed to only ask one question per post this is my main concern at the moment is the creation of the grids.

I can use a tutorial "looked didn't find one" or a guide written out "also wasn't able to find sadly" or even a premade asset. Thank you in advance for answers.