Allow us to define a blueprint which is a building sub-unit (e.g. a section of a wall or a floor of a multi-story building) that can be added to a building being designed. Alternatively, allow us to flag all or a selectable portion of the current state of a building design as a repeatable chunk for copy/paste-like behavior.
Yes, I realize that there are quite a lot of details and parameters to sort through in order to implement this.
No, I don’t expect this to come in the near future.
love the premise! I suppose I’d advise playing the “wait and see” game to see how the building tools get revisited in the upcoming alpha (whichever is next slated to have a building tool revisit)… 
Dredging up this thread because you can in a way do this now with my mod: [MOD] Structures+ v0.4.5
Just have each “module” in a building template then place them all down. Once they’re done use the merge tool in my mod to combine them into a single building. Easy 
This kind of works, but not if you want your templates to sit adjacent to each other like a wall segment might. You have to deal with that red no build zone so it doesn’t work.
Hmm, true. I’ll see about adding that to my list of ideas for my mod then. Chances are I’ll add a checkbox to the UI I’m working on for building settings so that you can turn the construction zone protection on and off as needed.
In the mean time, what you can do is leave a little bit off of each template where it needs to connect. Then when building just fill in the little piece of wall or floor by hand to fill the gap. Once that’s built use the merge again to combine them again into a single building.
Just added a feature to my mod now that lets you turn the no-construction zone on and off. It’s still got some bugs but it works and should suffice for what you’re wanting
In just going to start feeding you ideas. Everything seems to grow into a really good mod with you!