Most RP servers - regardless of theme - ship the same handful of custom locations. The reasoning is functional: certain gameplay loops need specific rooms.
For the broader mapping context, see the RP mapping overview.
Police Department interior
Holding cells. Booking. Briefing room. Armory. Sergeants' offices. Specific PD MLO designs vary by server but the functional rooms are consistent. Covered specifically in the PD MLO piece.
Hospital interior
Reception. Treatment rooms. Morgue. Surgery. Custom hospitals are often more elaborate than the in-game default. Covered in the hospital MLO piece.
Mechanic shop interior
Garage bays. Customer-facing reception. Tool storage. Sometimes a second-floor office. The mechanic-shop MLO is the most-handled second after the PD. Covered in the mechanic shop MLO piece.
Courthouse / civil administration
Less universal but common on heavy-RP servers. Courtroom, judges' chambers, civil records office. Tied to legal-roleplay loops.
Specialised locations
Drug labs. Underground criminal hideouts. Faction-specific HQs. Custom businesses. These vary heavily by server theme and aren't part of the universal pack.