Thanks for your feedback [:)]
I released a version 1.0.1 to fix missing borders when terrain smallest coordinates are negative.

The grid step is 50cm for the moment. It may be quite a large value but it seemed to be a good value for mid-size gardens to much larger terrains used for landscape purpose.

I may add some numerical fields in the future but sorry, don't hope that the elevation of other objects around the generated shape will be automatically adjusted. I think that it would too often lead to unsatisfying results along slopes.
Anyway, as rooms and walls don't have any elevation parameter, this is not even possible to program such a feature in a plug-in (Advanced Editing plug-in included).