I've considered adding siege weapons as units for my armybuilder, but am opting against it. Largely as a matter of bloat, but also because several units are hinted at already having (or being) battering rams and so on, and the overwhelming majority of them for the period are easy to make in a matter of weeks or days with the amount of manpower you'll have. The enemies in the lush, halfling-infested south may have a couple dozen magic-fueled hwachas and war wagons in lieu of the usual spellcasters, though.