How about this:
1) you can only have one building type at each estate (eg. only one sawmill / estate)
2) the more sawmill buildings you have operational in a region (an estate with one must be occupied) the more effective all of them are (if only a little bit)
OR
1) Have different kind of industry buildings for the same outcome, for example "(A)Logging Cabin", "(B)Saw Mill", "(C)Carpenter's Guild"
2) B only works if you have A and C only works if you have A and B or some such nonsense. You could also have D, E and F buildings, or it could work for some building types that you need two A's online for gaining a benefit from B.
3) Each of the ABCs would need to be in different regions (no realism there, pure gameplay choices)
The reasoning behind this is that a region could choose to focus on some aspect of region improvement, and if your estates all cooperate, you get a stronger bonus there but perhaps then need to sacrifice other benefits. A region could choose, for example, to really focus on the farming and food production and have it at 120% of normal food production. With a more balanced approach the region could have for example 110% of food production, 110% wood production and 110% tax income instead.
Then again I am really good at overcomplicating stuff. I quess all I am saying is that it would be really nice if the buildings one estate has could influence the buildings of the other estates in the same region, and that a lord who manages to have more estates filled could encourage industry chains for greater profit, but with a risk of breaking the chain if a knight leaves.
For additional fun, an industry building construction could work a little the same way as recruitment center construction does. You could build a sawmill, and it could be anything from 10% to 100% efficiency. If you are not happy with the result, tear it down and try again. This would make some buildings very valuable, and you would hate to need to tear them down for making room for some other type of a building. As with RCs, you could just choose to build a generic industry building cheap, and it is up to luck what kind of a building the game generates. Perhaps, as in RC construction, some special buildings could only be had this way.
Imagine the pain if you really had your estate trimmed to impressive perfection, and then the region lord changes and then he kicks you out. Or you lose your estate to war, and lot of the stuff gets burned down. You would end up loving your estates, and perhaps going to great lengths to save them from doom.
