This is something that bothers me the most about the settlement ordeal... Rebuilding.
With the updates and DLCs coming out, and such. I really want to reset my character and go through everything with the fixes, updated stuff, and so on. However, the only reason why I don't want to do this is because of having to rebuild my settlement stuff. It is very annoying and time consuming to do certain things in the building mode and get things a certain way, that I really don't want to do it again.
For example, fixing the walls in The Castle with foundation pieces... It took me a few hours of frustration to actually get that done, and perfectly straight...
So, Bethesda, why not give us the option to save an item's position and rotation (or a whole group of items) for future playthroughs? Like, in your current one. You pick them all up and use the save option to save their *current* position and rotation (the current one being where they were before you pick them up).
Then in another playthrough, there will be another tab on the main menu filled with all of the saves (mind you, each save is settlement-specific. So a Castle-save can only be built at the Castle). It'll require the combination of all of the resources needed to build everything and once selected, it automatically build that stuff in the placement that is saved, if you have the resources. (Ofcourse, it will not build if someone is in the way, to avoid glitches. Discounting pure static world items though, such as the ground, certain buildings, and so on for obvious reasons).