In HKN I went with Royalty, Nobility, Freeman, Serfs, and they recently got rid of slavery, because slavery spells had been used to make suicidal assassins and the guys in charge were teriffied of getting killed.
The Royals basicallt owned everything. That was the legal framework. The King OWNS the country.
Nobels were people he contracted to maintain the land for him. They also had obligations. Specifically because most magic users were noble, to have gemstone eyes of an elementalist, basically meant if you were not a noble, you'd get adopted by one. Futhermore, every Noble has a place in the country's army. YOU WILL SEND HALF YOUR FAMILY TO GO TO WAR. In exchange, they got the many many many perks of being a noble. They could "Own" land, in that, they wer the land lords for the king. They maintained the land, and kicked the taxes upstairs.
Freeman basically could not OWN anything, but they intern were free to make their own choices. So, all freeman were basically craftsman. They got to Rent homes, their place of work, etc etc etc. Yes a noble could be a dick, but the guy could say, "Fuck you. I'm a blacksmith dwarf. I gonna go over here now." While they couldn't own land, they could often be better off than some nobles, if they had enough money.
Freeman also usually covered the Aura Users. While you have your four classic Elements for the nobility, you also had those with grey eyes. These were people with aura cores. You could enhance your body only. Go faster, Heal. Get stronger, Wield magic weapons and in some very rare cases, shapeshift. Aura users usually happened when a Noble borks a normie. Instead of a elementalst, you got an aura user. (The king had a grey eyed son. Guess what happened.) So Grey eyes can be nobles, or even royals, it's rare, and they usually wind up independant mercenaries/knights for a noble/Royal.
Serf is basically, Indentured Servant. Not slaves, but they basically are caught in a cycle where they could never make enough money to get free. However, debt doesn't transfer to your kids, so kids can leave. This is the motivation to not treat your serfs like shit, because if someone else offers a better deal, you might not get the kids to hang around to replace the parents when they drop dead at 40.
See how I basically wove in the fantastical element to create a socio-economic structure?
Do that.