I think this is a really well put together mechanic, it's simple to understand and you quickly get into the eating-up buildings. I do think that the losing condition is a bit lacking, I don't really understand when I'm in trouble due to the competing things popping in the UI and the, to my personal opinion, too loud SFX sounds (in comparison to the music).
I think that focusing on fewer element in the UI or having less competing colors for most of them would help clears thing out.
I would have loved to have the tornado keep on increasing in size, à-là Katamari Daimachi, it would be an interesting idea to explore, having things scale really up!
Nevertheless, great job, clean and fun outcome!