If you really feel the need to stat such a thing out... lets see here...
Something six levels below his Might could be
used as a thrown weapon.
"Huge" gives a +2 to lifting & breaking trappings. I'd say a city sized bug has quite a few levels of huge, and probably Mythic Strength (+12 lifting) as well.
Lets say 4 Huge's & Mythic strength. That's +20 lifting.
Looking at the Lifting Chart, I'd say each +1 doubles the weight. For example:
+1 Most adults. I'd call that around 150lbs.
+2 Most heavy-set adults. Call that 300lbs.
It breaks down in a hurry between +3 and +7, but it's at least possible that's a typeo. But probably not.
For argument's sake, lets assume:
1) a mid-sized car (+9) weighs 1 ton (2000lbs).
2) Each shift after that doubles the weight.
3) A sky scraper weighs 100,000 tons (that's a very "brown" number... guess where I got it from)
So 2^x > 100,000. Solve for x.
x = 17 (rounding up to the nearest whole number). 2^17 = 131,072 for those of you playing from home.
And you need to beat that by 6 to use it as a thrown weapon. So 23.
And the mythic strength + (huge x 4) combo gets you to 20. So your super-bug only needs a might of 3.
But I'd just wave my hands and say "Plot Device".
Of course the big problem with throwing things like that is that you can't really throw them. They're hollow and designed to support their own weight while sitting on stable ground. Imagine a 5ft tall model of the Eiffel Tower made from popsicle sticks and Elmers glue. It's barely holding itself upright under its own weight when that weight is evenly distributed across its base.
If you grab one corner of such a building and lift, you're likely to rip that corner off and get a front row seat to watch the rest of it fall on you.
But lets say you pick it up successfully. Now you want to throw it (a Long Way). That means subjecting it to tremendous stress, almost certainly along an axis that wasn't meant to take it.
"Extreme consequences" just don't do it justice. Oh, some pieces of the building would go in the general direction you wanted, but most of the building's mass would break off and go in various directions, with a fair amount dropping on the head of whatever was foolish enough to try and throw something that fragile.
Yes. I said "fragile". At that scale, a skyscraper is popsicle sticks and Elmers.
If you really want your giant bug to throw something huge, try ripping out the side of a mountain. You'd still have some of the same problems, but you can at least argue the possibility with a straight face.
But I'd still go with "Plot Device". Dues Ex Bugina doesn't have to obey trivialities like "plausibility" and "physics".
PS: Zones? The building itself has at least one zone per floor plus one for the roof. If you're not affecting at least that many zones with your impact, You're Doing It Wrong.