I've had some questions about how to use the Apartment Room Markers, so I'll try to explain them.
In your Apartment you will have thee different types of areas. One area will be the actual Apartment, the other will be the space in the building you did not use and the final space will be the public areas. The last two areas need special markers.
The Public Areas include the Lobby, Hallways and any other rooms you add to the building. Say you want to add a Laundry Room or a Swimming Pool to your building, that room will need a Public Room Marker. Each room that you want to be visible but not part of your Sims Apartment will need a Public Room Marker. This can be found in Buydebug. Once placed the value of the room will be subtracted from the cost fo the Apartment, this is allowed and expected. The budget is only for the actual Apartment.
The other type of Marker is the Hidden Room Marker. Put this in any enclosed area you do not want to be seen or edited. Such as the empty space around your apartment layout.
Every single room that is to be a Public Room needs the Public Room Marker. As dos the Hidden Rooms. If there is no Marker that area is classed as part of the Apartment.
If any more help is needed or if you are stuck on something please do PM me.
Sidenote, if you are more comfortable with building an Apartment Building completely that is not a Highrise then do so! Those of you without LN can just disregard this about Spawners and just create a Building that would be appropriate for an Apartment.