Lavaman

I tried looking on the wiki for commands but couldn't find anything, but it's possible I missed something. Essentially, I want a way to select a region, then run a command that tells me how many blocks and what type of blocks are in that region. That way, I can build something in creative, get an accurate count of materials, then move things over into a survival build without much guesswork. If there's a mod for this, too, I'd happily take that. Thanks!