An RP server isn't just a different rule set - it's an entirely different version of the world. The custom locations a server ships are how that world becomes unique. We work through the mapping aspects of RP here.
For what players can expect from RP, see the RP server expectations piece.
What kinds of custom locations RP servers ship
The default pack: police department interior, hospital interior, mechanic shop interior, courthouse interior. Followed by per-server differentiation: clothing stores, tattoo parlours, drug labs, custom businesses, faction HQs, housing, social areas.
Most of these are MLOs – custom interiors that load during gameplay. Some are exterior changes – new buildings placed into existing areas of the map.
How RP mapping differs from single-player mapping
Shipped by the server, not installed by the player. Built for many players at once, rather than one. Must mesh seamlessly with the server's economy/jobs/faction systems. Must be able to support multiple NPCs and players interacting with it at the same time without ruining immersion.
Server owners don't ship their own MLOs; they commission them from MLO creators instead. That's why there's an MLO market.
What this looks like for GTA 6
Speculative, but an educated guess. Once we receive the PC release and the framework after that, we will see the default pack of MLOs either ported or recreated for GTA 6. The MLO market will follow. Faction-specific custom locations will come about as servers set themselves apart.
The first serious RP server mappings will likely stand up within a year of the PC release. Then there's NoPixel-tier polish, which is multiple years out. Server side, what a lot of new RP communities forget is hosting - GTA hosting setup guides go over the requirements and trade-offs that will ultimately determine if your heavy MLO pack runs smoothly under load.