Can't build/connect curved walls

Heya,

I'm kind of newish to building complex things and I'm having issues with building curved walls. The game won't let me make a curved wall itself by connecting it from one wall to another.

And if I take those ones who're already pre-built, then I face another problem, that if I remove some inner walls, the room gets a frustrating platform difference that I cannot change. So annoying. So I cannot use those to fix the problem of the curved walls.

Anyone who can help out? Couldn't figure out how to film during building with the sims camera itself (is that only possible in play mode?)