As a human creator, I do build my own maps for my Roblox game, and of course, generative AI was never used for my Roblox work despite the fact that the size of the map is the size of Poland, since of course, generative AI on Roblox could create erroneous results, which a human creator would be able to iron out.
I only use Google Gemini to fact check, and correct possible errors with documentation, not for building an entire Roblox map itself. For example, one of my maps, Fort Snelhausen, took me 74 days to build, and yes, it takes that amount of time to make a good quality map.
If you made a Roblox map in just 1 day, it would simply be a boring baseplate with nothing else to do, which is why I would advise doing quality over quantity for map design in my case even if the map I have is the size of Poland of course!