In Illyriad you are faced early on with the choice of repeatedly leveling up one production building, or keeping them all at the same level. Which one provides a higher production rate faster?
Ex: I have 5 farms, all of which are at level 0. Should I repeatedly upgrade 1 farm, or upgrade all 5 farms?
Disclaimer: Site link is my recommendation link.
Going on the data available to me via the wiki...
It is more efficient in terms of overall resources spent to level up your farms at the same rate.
The level 1 farm costs 20 of each resource for an increase of 1 (in terms of food production - it's producing 2 food, but that's only 1 improved over the previous level).
The level 2 farm likewise costs 36 of each resource, and increases the yield by 2.
So you can either spend 20 + 36 == 56 for a level 2 farm for a grand total of 3 increased food per hour, our you can spend 20 + 20 == 40 for two level 1 farms and 2 increased food per hour.
56 / 3 = 18.67 resources / food vs.
40 / 2 = 20 resources / food.
At this point, diminishing returns have yet to set in -- it's worth it to get all of your buildings up to level 2 ASAP, as they provide a better return on your investment.
However, if we carry on the math--
A level 3 farm costs 20 + 36 + 64 = 120 resources, the same as upgrading 6 farms to level 1.
Level 3 Farm = +6 increased food / hour 6 level 1 Farms = +6 increased food / hour. At this point, you get the exact same return no matter how you spend your resources. But if we carry the math one step further...
Level 4 Farm = 120+112 == 212 Resources and 11 increase in food / hour = 19.27 resources / food
If we spend those same 212 resources on 3 level 2 farms, and 2 level 1 farms, we get
208 Resources and 11 increase in food / hour = 18.91 resources / food
It's slight, but by this point, you've gained the same bonus for slightly less resources than if you had focused on leveling a single building.
Keep all your buildings as near in level as you are able for the best efficiency.
The most important aspect here is in terms of how often you are able to log in.
Suppose you are only able to log in once per day, and therefore issue just two build orders per day. In this case it is obvious that the best approach is to concentrate on levelling up the highest level building that you have the resources available to upgrade, as this will give you the greatest return on the two build orders you have to use.
If you are able to log in more often then this is much less important, and the next greatest restriction will be in terms of the basic resources you have available for construction - but here there are several things you can do to help you. Firstly, your caravans can gather some basic resources from the map. Secondly, you can trade for basic resources by producing tradable commodities - like livestock - or using cotters to harvest generic mineral and herbs.
So with that restriction dealt with, the next most important is in terms of the time it takes for your build orders to complete. The Architect's Office building will reduce building times, or one can spend money on the game - and reward the game's creators - to buy prestige and use that to auto-complete build orders.
I don't know how the Maths works if you do not use Prestige to speed building orders, but if your aim is to eventually level them all up, and in the short-term you can supply your basic resource needs by trading/gathering then it doesn't actually really matter.
In the end I decided to level up one of each resource field to level 7 first, because this opens up research opportunities for extra buildings, and building those buildings opens up further research opportunities for other buildings...
