Build linkable wall similar to red alert(game) in unity

For this project i need you to be able to simulate the building of a wall in unity 3d. The wall logic should be similar to that of c&c red alert. On touch and on click for the input controls. Can use basic cubes for the wall instantiation. Touching near the edge parallel to the wall will lengthen it along its axis. Touching near the edge but perpendicular will create a perpendicular attachment.