Update: reducing the global stone effect is needed, as you can achieve negative building cost which prevents building anything at all.

@MaxRavenclaw Fixed the effects so it has the prefered localization

15% global reduction would be more than enough for stone, also you could use both a local and a global effect (like -15% local and -15% global), especially since the UI would then make sense (no more 0% line).
Don't forget we can already get up to -12% building costs from general appointments.
Roads are mostly worth it for movement speed and replenishment rate tbh.
Also what MaxRavenclaw said.

By localization I refer to the text that's displayed in the UI (dependent on what language you have set in the game settings). You're using existing modifiers which already have some localization attributed. It's been a while since I wrote that comment, but IIRC the text displayed for the modifier of the Level 1 buildings best described what it did, while level 2 mentioned "local" effects (though they applied globally), and level 3 modifiers I don't remember what said.

For example, I believe mod_unit_recruitment_cost_land_all is an effect that's always tied to a province level modifier and as such the existing localisation describes it as local in the text in the UI, whereas recruitment_cost_mod_land_all_global is related to a global modifier and is referred in the UI as such. So you're better off using recruitment_cost_mod_land_all_global for all levels of the Iron Mine, IMHO.

@MaxRavenclaw thank you for testing! Just before I go ahead and change that up, please clarify what you mean with localisation?

@Smiley thanks for the feedback. The Stone is really OP, making it as strategic important as Blacksmiths and craftsmen. My thinking was, by the time you reach your 2nd stone resource, you'll be like a turn away from triggering Sengoku, and from the Sengoku its like 10 turns to victory, really skewing the investment horizon for lots of buildings, but with a whopping 60% discount, its still worth it to invest rather than just pour everything into armies

This is a great mod, but I feel like the Stone one is really OP and you should decrease it the same as the other ones; getting 2 means a potential -60%. I really like the balance with the other ones; potentially I would make it -10%, -15%, and -20% to make those early levels feel more impactful.

I've tested and can confirm that all effects work as intended (globally), but I'd advise you just go with the effects you used for the Level 1 buildings as their localization fits best. Level 2 effects mention local effects in their localization (though they still apply globally). Level 3 are hit and miss.

Really makes a new campaign feel fresh with your mods installed :D

@MidnightWinter I wouldn't know how you could reduce building costs apart from capturing stone mines and the odd chi research. as far as stone mines, I think there are 3 of them on the map. so they should only total up to 90% and never push you into negative prices. same for iron

So I just tested this mod as I used to use Global Resource Effects but it seems all of the Global Resource Effect mods have this bug with Shogun where if you build too many of these specialty buildings prices end up in the negatives for some buildings making them unable to be built same goes for units. For instance with this mod every single building is greyed out and cannot be built unless I had a negative value of money. Rather then the building just costing 0. Mind you this only happens once you've conquered half of Japan and are basically endgame but still.

Interesting, may give this a try on my next play through.

Final level for timber and stone work at least. haven't checked Iron yet.

Notice how the effects in the factionwide tables are different per level? Yes I'm totally using you guys to user test for me. I didn't have all the test cases set up to check myself and that would take a long time. If anybody notices any off behaviour i'll fix it and update.