Create your MLOs with Codewalker
Codewalker is the professional tool for creating FiveM maps, MLOs and environments. It allows the placements of objects via drag & drop! If you want to place an object (e.g. a bench on a street), you can do this. Save your file as .YMAP to import it to your server.
Codewalker requires the PC version of GTAV installed, and .NET framework 4.5.2.
How To Tutorial
If you want to read a tutorial about this program, you can find one here:
https://forum.cfx.re/t/how-to-map-an-interior-and-stream-it-in-fivem/59488
Creating own maps (YMaps)
Codewalker allows to extend your map. Open the program, start a new project and be creative. Be careful about area complexes, do not delete them. Test your maps consistently, you might experience some issues (like crashes). However, the most stable maps creations are MLOs. Be sure to always make backups of your server and maps.