Apologies in advance if this is already suggested...
I haven't constructed much in the game but I think I'm getting the hang of the building. One common thing I need but don't see is a "Slice" option. Quite often I find myself needing a half cylinder, and to make it happen it takes a few parts rotated and microplaced to make the illusion of the half cylinder. All we need is a slice option that lets us "remove" half or more up to 95% a fuel tank interstage or whatever we only need half of. Half round to square is a very common intersection on a lot of ship styles in many places.
We also could desperately use some round shapes. A sphere. For now it's two cones and flattened fuel tank to make a somewhat round sphere 🙈
@AverageJoe Ahhh I see what you mean. But yeah I agree we need more shapes, especially spheres imo, along with the vertical fill / slice feature included in the recent SP update.