Do you mean just random build structures that are built when the seed is generated, or actual structures you've built yourself?

Because if it's those auto-generated buildings, you'll see the same formats used across all world seeds, with not a lot of variety. Though it appears a handful of new ones were added with H&H.

We created a new world and new characters for our post-H&H playthrough, and definitely haven't encountered buildings that we built on previous worlds.

That would be a neat feature though, old buildings copied to new seeds in random locations, but in a run-down state!