It's because it's built on a slight hill and it goes with the flow. To get a long shot pic, I'd be standing in the woods and you'd only be able to see it through the trees, but I'll try. The concrete was swept to be in sinc with the earth. This way, it won't compact itself and explode, just slowly crumble in a big storm. So you'd be standing in crumbled concrete with a metal roof over your head instead of a sudden crushing. Because who wants to be suddenly crushed.
Pretty much anytime I guess, as long as you promise not to call it a lawnmower. Oregano and chives grow back too, after you cut 'em down.
And I do like you better....
I knew you did
Lawnmower eh? I get it now...duh!
I sincerely hope you engineered the slab properly and do not get crushed by it. That would be a wild storm.