In Planning Mode, you would "build" ghost versions of everything you can build. These ghost versions are white/gray translucent with no collision (other than the ability to snap - you can walk through them) to clearly indicate that they are merely plans, not actual buildings, though they still can be aligned to each other. When you build one of those ghost buildings, it is automatically added to your To Do list. If you deconstruct a ghost building, it is automatically removed from the To Do list. You can fully plan out a factory from the foundations up, plan out conveyor belt paths, power poles and wiring, everything, and can make edits to your plan as you go and the To Do list will constantly update itself and once you're done the To Do list will show you exactly what you need and how much you need to build it all. Once you start building the actual buildings, they snap into the ghost versions of themselves to make placement quick and easy. Once a ghost version has been replaced with a real version, the ghost version despawns.