How do games spawn menu areas or character creation rooms for every player?

In the Roblox games where you have a 2D menu but it is in front of a 3D background like a lobby or something. Also like where characters are put for character customization.

How is it done? I thought it would be spawning a model at a random position whenever a player spawns but there are a lot of problems with this: Some rooms might overlap, some rooms might be somewhere you don't want them to be etc.

The background could be a picture of the room or the background is a built room. Although there would only be one room on which the players see.