The rules say any empty pizza boxes in our house must be turned into terrain which can be used for multiple projects.
Now my 8-year-old son is deeply interested in our dieselpunk post-apocalyptic world, "Panzermunda" - basically 1940s Mad Max with mutants, cannibals and zombies, and WW2 tanks as the primary transport. I'm working on homebrew rules which are basically small-gang skirmish Flames of War; with individual tank crews almost like RPG characters. My son likes to discuss it, which helps me 'flesh out' the world. His questions include: "Would a Lee/Grant be best cos it has lots of room to sleep in - or would a Sherman be best cos it has easy-to-get-parts?" "Could a cannibal break into a tank when it's sealed up?" "Do the towns have castle walls or just barbed wire and landmines to stop the monsters getting in?"
When my daughter says sceptically "Huh? Why do you guys have mutants and monsters with WW2 tanks? My son loftily replies "The poison gases and chemicals from WW1 caused it, of course!"
I do need some 15mm mutants and zombies but postage to Australia is usually brutal. Is there any good 3D prints?
Now roaming tank pirates and scavengers often loot the ruins of the factory cities, which can also double as WW2 ruins. My wife whipped up some templates in MS Word and I commenced cutting and taping. Our feral neighbours left some flyscreen on our lawn so it served as a window/skylight grilles. I probably used the equivalent of a $5 can of Bunnings spraypaint so these buildings aren't totally free, I guess.
The templates mostly made small workshops and machine sheds. I have yet to do a big factory as I am running low on pizza boxes and I felt lots of smaller LoS-blocking 'scatter' terrain all over would be handier to start gameplay-wise with than 2 big factories in the middle and 98% bare table.
I chopped up a few with clippers for battle damage and used flyscreen for security/skylight grilles.
My wife did these two above as a test run for a smaller two-storey factory; but had trouble fitting it onto an A4 so it folds out - the next 'proper' factory will use 3 A4 sheets and be stuck together in several bits; also they will be about triple the size for a more "Enemy at the Gates" size large factory and tanks will be able to drive inside I think.
As usual, my focus is quick and table-ready terrain - I had only two hours to make a table of terrain from start to finish. Turning each building into an artistic masterpiece is more the reserve of Youtubers and the independently wealthy, not a working dad. So apart from gluing on the screens, just a quick squirt of grey/brown/black spraypaint and it's ready to go. If I had time, I'd bog the joins/cracks, use PVA (not tape) and add some texture (maybe a dusting of flour and PVA glue to make the concrete 'rougher' as well as using matchsticks for doorframes/windowsills.....
....But I'd rather just have more terrain. Next time we get pizza: I need two big mega factories to finish this table, then begin a table of 'suburban' buildings; not sure if I'm going terrace houses or Soviet apartments...