Destruction can be difficult, but I think you're going to have more trouble finding a good background for 34. Look at 11, and imagine the perspective of the ground plane, continuing out of the room and on to the horizon. When looking for your background the ground plane needs to line up with a similar perspective. This is the same for most collages, but the issue here is that you have a second plane to worry about instead of just the ground plane, since she's sitting down. The seat part of the chair should line up with a rooftop (i.e. you should actually be able to see the rooftop itself, not level or below). Try to picture this second plane, of everything at the same altitude as this rooftop, onto the horizon. You can probably find a background that works, just keep in mind those matching planes in combination with matching lighting. Now with 34 you're throwing in a third plane (the ground, the chair, and the desk), so your options are limited even further (especially if you're wanting her knocking into another building, too). But if you can find something that matches these elements, it will work all the more to your benefit instead of against you in making a convincing collage.
As for destruction, I usually play it by ear. Generally what I do is>look for demolition pics until a similar building to the one being edited is found>adjust new layer with perspective tool>adjust color curves and light levels>erase along the edges with a mask and textured brush
Sometimes you can just copy-paste an existing building in the BG and warp it slightly to suit your needs, like if you wanted a building to be buckling under the weight of a sitting giantess. I guess the trick is getting your effects to work together. Dust can work well covering seams between demolition layers on buildings, and you can use rubble on the ground to completely cover structures in problematic locations.
Sorry for late response, got more tips if you want, at text limit with this post tho