And that′s his issue I think. That he can only scrap the crumbled ones, but not the rest. Not to mention that this foundation is actually quite limiting. I haven′t unlocked all build options yet though. I wonder if you can build foundations yourself. All that concrete must be good for something rite?
There is a concrete foundation, just very oddly sorted under "Structures - Wood - Floors", at least on the PC version.
One way is through "Picket Fences" I believe it was called. It gives you new buildoptions. And the other is through local leader. However, I wrongly assumed that certain stuff would only be visible by taking said perks. In that I was wrong.
I actually just spent all day checking out all the settlement locations so I could make a video on the best ones. I think your best bet would probably be Spectacle Island. It has a few structures on it, but the place is so vast that you can just make your own flat area to build on using concrete foundations. Honestly, I was kind of disappointed at the options we're given overall. Many of the settlements are too similar in what they have to offer.