So many eureka moments tonight! 
I am now at the point where I feel the basic system for the buildings is done. It starts by spawning a Foundation block, then adds a random number of floors on top, and tops it all off by adding a roof appropriate for the last floor-tile - that bit took me SO long to figure out, but I actually managed it in the end. I ended up scrapping the floor-height thing again (but thanks for input, guys ), and went for a Socket-based approach instead, so I could have floors of many different heights, further adding to the randomness. Here’s a shot of a quick (not yet procedural, mind) layout using my debug blocks:
Welp, that’s the easy bit done, I guess. Now I should really cracking on that road-thing. Yipes. No clue. But guessing it’s something to do with splines… xD