i found a video wich shows what i mean with ghosted building, this have a futurerustic look, the important thing for me is that you can mod this feature as you want. so here it is, also you will need to look at the builder units the SCV's when he build, there is both a model shown when he selects a building to build it and when he places the building to build it. so when selecting a building icon to build a model of the building is shown on the gamescreen then you chose where to place the building, now if the constuction site isnt in range, it will place a slighty modifyed version of the model, perhaps with a simple transprancy and overide colour option for it
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the video shows exactly what im talking about but you will need to see the entire video.