I've been trying to get my head around how to create a selection box for a selected unit in a 2D top-down type game. When you click on a unit, a small box would appear around that unit based on some sort of box-size.
I do not know/understand how to either calculate the size that box needs to be, draw the box (have an object under the game object that is sized appropriately with the selection box texture?) or how to make the selection box adjust it's size/shape like in this gif: http://i.imgur.com/xY7XW6C.gif
I don't expect anyone here to hand feed me what I need to use, but some idea of how to go about doing this in Unity (starting from the smallest, and most simple thing, like just making the box) would be very much appreciated.