My apologies in advance for my weak photoshop skills.
As I mentioned a while back, I was intrigued by the suggest of a Mutant Future reverse megadungeon, i.e. a big ruined city. I could, obviously, just go the “normal fantasy dungeon with rivets” option and I’ll admit that part of the draw that I have for this is just that it would be something other than elves and dwarves and orcs all over again but still have the OSG megadungeon experience.
But, if…if I were to do the reverse model, and do the post-apoc city option, here’s what I would do.
I’d create terrain tiles, 6″ or 8″ across of random post-apocalyptic terrain, maybe nine or sixteen of them.

So, a crudely-rendered version might look like this:

Then, as the PC’s enter each “block” or “region” of the reverse megadungeon, I’d make a layout like so:

With a lot of variations available, and maybe some one-shot terrain to represent special encounters, you could create an entire city of unique blocks.
And I’d be able to scratch my hirst arts terrain itch and my OSG roleplaying itch and my sci-fi post-apoc itch all at the same time.
That… is also the best way I’ve seen to do 40k Cityfights. Just take a bunch of terrain, maybe make some long, flat road squares that are maybe 4″ or 6″ wide to go in between each terrain piece, and off you go!
We tried to do this with 2′ sections, with each section being it’s own city ‘block’, of a building or two each. The pieces were mounted on some thick, pink Styrofoam, and you’d be able to mix and match each game. Alas, our building making skills are (still) mostly regulated to cardboard and styrofoam…
i still owe you a building or two. I should sit down with you sometime and discuss how to pretty up that cardboard and styrofoam.