So you can actually design new buildings to be enter-able, with full interiors, but most people don't because it's an extreme amount of effort and very difficult compared to the old designer (in the old one, they all had interiors by default since that's how you placed the rooms)
Some few Haxus building designs and Phoenix ones have interiors, but most don't
Some few Haxus building designs and Phoenix ones have interiors, but most don't
What even