This is a very fun game. its free and its multiplayer (classic version).
you can run your own servers and it's pretty beast.
create what ever you want, towers, sculptures, grottos, underground tunnels.
example:
I think MPGH should have there own server, it only holds up to i think 40 people per server and its really fun, different ranks such as Builder, Advanced Builder, etc.
each rank means you can give a new map, for only that rank and above to build on.