NO, no, no. This si how i would do it. A unit constructs a building witch needs to be rounded by the wall. Then you create say 12 dummy units and order them to build a wall on a point with polar offset that is equal to 360/n of dummy units(of wall units) you assign those dummy units into an array and leter remove them from the game. It would also be a good idea to null the unit values inside the array once the construction is finished. It's not that complicated.