I like the idea of large buildings and small buildings.
Lords could be limited to X Large Buildings in his estate (paper mill, grain mill, Mine, lumber mill, or wathever gives bonus to the region as a whole) and the knights would be able to build small buildings in their estates (hostels, taverns, shrines, or any other ideas that could give more gold our other benefits to the knight) and one large building.
If the lord want have more large buildings he will need more knights, and he will not kick a knight for no reason, since he needs the building there.
With the small building the knight will be able to have a small additional income, or other benefit that he will chose. This will personalize the character estate and give something to do when you are a knight. I saw something in the realm about Statues. Maybe it could fall in an "artisan" small building. Then if you want a statue you will need request this service from a knight who have it, or have one in your own estate.
I like the idea of things that only who have a kind of building/resource may produce. To me this provide interaction, and interaction is good.
