Ah yes, Roblox. It's like Minecraft with a bigger focus on creating.
As a comparison, in Minecraft you would have to take things block by block.
In Roblox you are blessed with god like powers. You don't have to worry about single bricks, and you can save the structures you've built.
Actually, it wouldn't be that hard to make a miniature Minecraft using Roblox. You can make pretty good sized sandboxes by resizing the baseplates.
Also, scripting! When you learn how to script virtually anything is possible. You can make set pieces, objective markers, vehicles, nearly anything you can think of.
If you like creating stuff, play Roblox.