-placing buildings in PB1 often felt like fighting the UI, forced into using exploits to level the terrain, placing buildings to carve out a single voxel point off a hill, one at a time, then quickly deleting them before your colonists build them, until the building you actually want fits... Instead: a scaling placement cost system, would simplify this for the player a lot, and feel much better. If a building is halfway inside a hill, just make it take longer to build, and require 50% more metal perhaps, representing the added structural supports needed to build halfway underground. Resulting in cool bases that poke out from the hills, shire style (which is probably how real bases will be built on Mars for protection from radiation) ... maybe the player could even choose a commander modifier that reduces these costs if they really want to build into cliffsides for aesthetic reasons... maybe it would confer a small insulation bonus reducing running energy costs since the building is less exposed to the atmosphere, or lackthereof.

-I think it would be really cool if the bases you build could contribute to some kind of persistent accumulation of infrastructure on the planet, and/or community goals. Like X planet has very limited manufacturing capacity atm, so players could prioritize building major manufacturing bases designed to import ore and export construction components, reducing the cost of component imports by a small percentage for all other players?... Something like that could make each base feel like so much more... Like you're building towards something. Cooperating with other players. Even if it's indirect. Making it feel like your work is fulfilling a need.

-some degree of verticality/density is cool, and logical in a hazardous environment... not sure how viable having multiple stories would be from a UI standpoint, but it would be cool and fun to have basements for some buildings. Maybe with tunnel connections, like some kind of maintenance routes, that can be used in emergencies. Maybe building placement could toggle a foundational basement construction section or not, depending on if you have the resources to invest at the time... while building a basement later takes longer and/or costs more.

-oxygen management. It would be cool if in an emergency, you could seal off sections of the base, and pump all the oxygen into the remaining active buildings, improving saturation, and buying time for you to fix the problem. This could create fun scenarios imo. Generally having multiple states of emergency responses to buy time keeps the tension high, while not killing the player outright/ending the fun.

Feel free to dump some more ideas here