In urban centres,there are too many arrestors so much so that you would not need worry about being struck unless yours is the tallest building in the neighbourhood.Case in mind are the overhead cables where the top most line is an earth line.Stand alone units in sparsely populated lightening prone areas though would need your kind of attention.At most,a two feet copper rod propped above the tallest point of your building,followed by a tag copper wire or band and dug deep into the ground will be good enough.In some instances,the tag can be a simple mild steel flat bar well anchored to the ground.Some vital and sensitive instalations may require more than that and the same also applies to residential houses.Where you do not want to take a chance,the tag line/flat bar can be attached to a rectangular copper mesh of about 2' x 4' depending and the same covered with a layer of "makara" before topping with ordinary soil.....It"s all a DIY thing.