Just a random idea on Fortress construction...

[Tuidjy]

Speaking for myself, I build forts where I need them, without caring what kind
they turn out to be. In Dominions II I would always choose the watchtower, but
in Dominions III I find myself using troops a lot more.

I wish we would get a choice of which castle we would built. Some nations could
have multiple choices of castles in some types of provinces. Sometimes I want
a fortified city, sometimes I would be happier with a watchtower. Actually, I
would be happier with a watchtower 90% of the time :-)

[Lazy_Perfectionist]

Sometimes I go for the cheaper option, Sombre. But sometimes the expensive really does pay off. If your dominion creates a real harsh supply penalty, and you're playing Agartha in a cave fort (high def, low supply & admin), you can hold out forever, not needing food.

But fort strategy is another thread, to paraphrase Alton Brown.

On the original idea, of tying resources to fortress times, I don't like that. What if you're on one of the maps with fairly homogeneous types of terrain? If you have to expand onto wastlelands, when will you ever be able to get another fort up? Meanwhile, Agartha with a couple iron mines (i've had two in the same provinces) could throw up cave forts at a ridiculous pace, garrisoning them with no-need-to-eat Pale Ones.