Just some ideas for locations.
Firstly, natural industry.
Lumber Mill: Located in forests, on roads. Often have large areas of stumps around them. Contain a great deal of both logs and cut lumber (2x4s etc). Certain tools available, obviously. Probably has two separate outbuildings; a workshop with nonfunctional machinary and some tools, and a separate building which acts as a lunch/break room, and probably has an office or two.
Quarry: Really a flavor thing. A section is cleared out to bare rock, and there are large amounts of loose stones laying around. When Z layers are implemented this could be modeled as a pit. A small structure might serve as a break room with offices. (Note: Add dumptruck as vehicle, spawn them here occasionally). Certain crafting materials might be found here, if things like clay or unrefined ore are introduced. Also certain tools.
Farms: Farms are already in the game, but I’d like to see them changed. Right now they seem like glorified gardens, when really farms should have huge swaths of land encircled with fencing. A single farm might be as big as a whole town, just endless corn and wheat and grazing pastures. We’re already using huge swaths of open empty dirt+shrub terrain, why not use some of it for proper, actual farmland?
Secondly, industrial parks. Not as a structure but as a unique area where a new set of industrial buildings might be spawned together. These areas would have relatively lower zombie population but be populated with other enemies like blobs and CHUDs and other such terrible things. Things like toxic waste dumps and extra-dimensional beings might be more common here.
Warehouse: Located around other industrial sites. These typically do not have useful items in them, they are often completely empty, but sometimes contain stockpiles of very specific items. If possible, tie warehouses to industrial sites nearby. Ie, a warehouse near a lumber mill might contain a stockpile of 2x4s. Warehouses are locked, have no windows, and have heavy doors that must be picked.
Factory: Located largely in industrial parks. Factories are large buildings that contain a lot of inactive machinery/conveyor belts, and large numbers of very particular kinds of items. One factory may have a huge amount of RAM available. Another might produce nothing but cans of spam. The amount of stuff in them should be considerably more than you’d find in a shop, but not so much that the supply is effectively limitless.
Refinery: A very large industrial area with numerous interiors and interesting loot. I see this as a large project meant to offer some exploration and danger. Such locations may include a private security building with an armory, plenty of hazardous terrain, dark tunnels full of CHUDs, and potentially connections to the sewage system. Gasoline would be plentiful here, and perhaps a new type of monster made up of animated crude oil could be introduced. Or just lots and lots and lots of blobs.
Basically I’d just like to see the Cata landscape industrialized a bit. Industrial parks would be a whole new area to explore that differs in many ways from the suburban towns we see now.