I think it would be cool if Hero's could build additional money making buildings such as farms, oil platforms etc.
There may even be some specialty buildings which serves as a shrine. Ranger could build a lumberyard providing +5 strength +2 movement for wood units (elfs, unicorn, wolf rider) or Horse Lord building a blacksmith same for horse units (light cavalary, heavy cavalary), Paladin could build a temple for holy units (Crusader+?), Assasin could build for assasin units (Medusa, Ghost etc)