I would like to share some strategies for upgrading Money Buildings.
Early in the game I found out that RIO index is not worth to follow, don't know who is using it even in the real life, since there are always other factor to consider an investment
I am using slightly different approach when buffing my Income.
First of all, common sence:
Cottages change a lot the Income per Hour but are worth it only up to 5th-10th level when you need to buy less expensive units and 20 gold/5 minutes is much appreciated. My Cottages are at lvl 7 at the moment because of the silly quests I got and I dont intend to upgrade them any further.
I am using an Index number that I have labeled "Upgrade Gold Gain per Hour" - it means how much gold I will gain per 1 hour of upgrade time.
I am using this Index to compare all buildings and to choose that upgrade that will give me most gold gain per collecting hour for the least upgrade time.
Or in real life economic it just means "How to gain most money in the shortest time considering I have enough investments" - Upgrade money is no problem in Kingdoms age and this is why Return of Investment Index is worthless. You always will have more money than you can spend on upgrades if you are somehow inteligent developing your Kingdom.
A great factor in spending money in KA is the Vault size - there is a danger keeping large ammounts of unspend money in game. So better use them on upgrades.
I.E. Upgrade Shipyard (Collect in 18 hours) from lvl 1 to lvl 2 (500 gold to 1000 gold): upgrade time: 27 hours, gold upgrade 500 gold/18 hours, Upgrade Gold per Hour Index = (500/18)/27 = 1.03
This compared to Stables (same collect time building) from lvl 1 to lvl 2 gives you an Index of 4.03 so it is better to upgrade your Stables first. Of course your Stables could be higher than 2nd level at the time you have build your Shipyards so I always compare the next levels of any two buildings I want to upgrade.
This assures more gold gain for the same upgrade time and faster money growth.
Next thing I consider is the gold "step" between any two levels of upgrades. I.E. Shipyard 1 to 2 gives you 28 gold/hour (500 gold / 18 hours) but Shipyard 2 to 3 gives you 14 gold.
This "gold gain step" applies to any building: upgrading any building from 1st to 2nd level gives you double the ammount of gold than any further level, so I always upgrade any building at least to 2nd level and if the UHG Index is lower I leave that building without any further upgrades. There is no need to upgrade the Inn pass the 2nd level because the gold gain compared to the hours needed for the upgrade is unsignificant compared to the Leatherworker, and looking at the numbers there is less gain from Silos pass the 5th level than again Leatherworker - even if you dont understand the concept, just following the numbers can give you the right idea that it is much more worth it to upgrade Leatherworker than Inns or Silos. You will invest less hours for more gold gain upgrading the Leatherworkers than Inns or Silos.
Of course the UPH Index is worth to follow pass your 10th level, till than you dont have much choise upgrading buildings and is best to follow when camping. UPH Index does not apply to the short "bonus" upgrade times at the start of the game - like 30 seconds upgrade or 15 minutes upgrade.
I started to use this approach because sometimes the gold gain from some buildings looks very aluring but if you dont pay close attention to the upgrade time you cant understand that it is not a real gain and it is better to upgrade a building with slighlty less gold gain per hour but in much shorter time.
Again, for these that do not fully understand this concept:
1. Use your common sense - check if the upgrade time is not at 4 am, because it is not worth it to lose your sleep even for KA
2. Check if you have enough money for the next Vault upgrade - this is more worth than anything in the game, after you have maxed your Vault, you are free to follow this strategy at full.
3. Make a short list how many times you can milk all of your buildings, I can collect money from Libraries/Butcher Shops only two times a day so I consider these buildings 12 hours not 8 hours and I have changed their values in the Excel file from 8 to 12, but all of this is up to you. UPH Index is best worth it to compare the buildings in the same group or close group of collect hours - libraries to butcher shops, inns to silos etc.
4. Choose the building that will give you the highest Index and upgrade it.
Make a list of at least 10 buildings and than see if their finishing time is in a comfortable for you hour of the day, I have another table that calculates all of this but I dont have the time to clear it from my datas and to post it here.
For the time being I am posting only the Excel file that compares all buildings to their UPH Index.
Just to show you how good this works, I have a Kingdom of 40 tiles, Vault of 220 k, more than a million spend on equipment, more high priests and flaming catapults that I need and more gold from bazaars/merchant caravans/farms per hour than I need to open an event chest for my level (which sometimes is a big limit - so I do not rely on these buildings for developing my kingdom and in the same time I always get at least 15 gems from free play using game gold with no worries that I limit myself). Every day I am always at the edge of my Vault limit and usually at the end of the day I spend gold on equpment or more units because someone can take it from me. Even my Defense density is more than 170 I dont want to donate gold to better players
p.s. Actually this Index is the real Return of Investment Index, I cant understand why someone has decided to just divide the upgrade cost to the collected money and has labeled this ROI since this excludes so many other factors from the formula.