I have been experimenting with settlement building in the game and I am disappointed with the lack of certain building pieces. I think we can all agree on that and we should appeal to Bethesda to include these via a future update.
1: windows. There are absolutely no walls with window frames. Apparently settlements are built for recluses who want a vitamin D deficiency. It's possible they thought there were enough holes in the wooden walls to make up for it but if you want to build a metal shelter there are no windows at all. They really should be included because we gamers already have enough problems with Windows. (Ba dum tish)
2: doorways in flat walls. The only doorway pieces so far are the kind that are designed to go only on the outside of the wall. There is no way to divide up the indoors without huge gaping holes.
3: better gates and a fix for junk fences. My first major construction project in the game was a pair of towers with a gate between them. The only decently sized gate was the one from the junk fence category. I had a hell of a time doing it because some idiot made it impossible to neatly line up such pieces as they simply don't connect to each other.
I would also have a problem with the wooden floor tiles. Last night I was trying to build a two-storey shack using the wooden stairs and the small floor tiles. When I looked from the outside I saw there was a gap because they aren't quite as thick as the upper floor tile.
I also think spiral stairs should be considered the next update, and someone was played a lot of the Sims, I can tell you they save a lot of space.