This came up when the game started to lag slightly. With too many buildings in progress, speeding up time lags a little, and I was trying to figure out what is the problem.
That is when I noticed that 1x1 road piece is seen as one building, and is built separately by different number of builders. Perhaps, it's better to do the road alike to terraform tool, when one large road placed at a time via dragging your mouse if being counted as one building instead of, say, 30 small ones?