Something that’s pretty basic and requires building is making an obby, you can decorate it and other stuff. It’s pretty simple since you basically just need to move blocks or have kill blocks too, but that’s pretty simple! Also, it’s appropriate for Roblox and most new builders should be able to do this.
The year is 2039. A zombie virus broke out from Salt Lake City, when the salt was dug up revealing tons of gasses which were toxic to humans, thus resulting in viruses spreading. As the virus spread, the military was quickly overrun by the hoards. Citizens began taking shelter and building to survive each day. They stockpiled weapons and food. Can civilization keep going on?
Sorry if this lore is not realistic, however I just thought of it.