>And what happens when the player does not select a flat surface? You get an error message "I can't work here" or similar?

In my mind the clonk just stops.

If we at some point decide to build this we can concept the details. For now we have enough work :). Well, but just copying the CR behavior would give back the possibilities I mentioned: Of course some Clonks would die or fall down cliffs if they are not watched from time to time, this would probably not be very newbie friendly. Still the commands made controlling multiple clonks possible. If there are no commands their use gets reduced to equipment and position (which is still enough to justify that we keep some support to my taste).