Me and my group understand the Grid based movement concept, but are lacking in how to make tiles based on that movement. is there a way to know how big to make a tile vs how you move or is it just all feel and guess? We understand collision when you hit a wall, but don't want the player to miss out on something do to a bad tile. Thank you in advance. We are using Unity as well.

In a game with grid movement you probably don't want to be using collision and instead some way to know what is at each grid position. 

For example:

If position trying to move to is a wall, player cannot move there.

My take on this is to move the player by the tile size, so if you have 5 unity units (?) long, you move the player 5 unity units. I do this by resetting the velocity every physics iteration, so it goes: key hit, velocity = (0,5), move, velocity = (0,0)