Thank you for the response! The link you gave me was actually one of my references before I built my building but I forgot to bookmark it, so thank you for that. I actually fixed the elevator problem- it has something to do with the floor.
Now, I still have my NPC doors dilemma. Is the correct "facing" of the NPC doors a very sensitive factor on this? The arrows are pointing outside (meaning away from the door). I've read somewhere that it may take few sim weeks before NPCs start living on these units so I have to be more patient, but I just want to make sure that I did everything correctly.
Also, I don't know why my bill is higher. I built the EXACT penthouse unit from my previous premade building, and my usual bill was around 1.5k.. now it is around 3.5k. I'm pretty sure I designated the public markers on the lobby and other amenities, so I don't know what made the bill higher.
I've also read on the link that you gave me, that OP puts public space marker on the lawn-- I don't know if that is correct, though. I think I can live with the game not detecting the penthouse as the actual apartment unit of my sims though (for instance, when I click the "home" button, it zooms to the entrance of the building, not to the penthouse floor *sigh*), but if someone knows how to fix this, I'd really appreciate your help.
So I attached the screenies of the 2nd floor where the NPC doors are and the ground level which is the lobby, for reference.
Anyway, thanks again for your help.