...are you just wasting time?
I recently starting plotting out a terrain build for a game, but partway into it I experienced misgivings. The idea was to make some terrain for a specific battle where the nature of the layout is pre-defined by the module. Was it really worth the time and effort to put this thing together for a specific session? It would take most of my evenings between now and then (I would really have to rush), and it would likely only get used once. Further, it would mean I was concentrating on getting some "prop" ready instead of prepping to run the actual session.
In the end, I'm opting to ignore the terrain and try to get my head ready to run a fun-filled session where I keep the action moving and the players on the edges of their seats.