When I give him a consequence, should it be for not making his bed or for throwing a tantrum about it?

​If your son has a tantrum, give him time to compose himself by using a calming-down strategy. Teach him ahead of time ways to remain calm. Then, when he's calm, give him a consequence for having a fit (a time-out or take away a special toy). Later, you can ​instruct him to make his bed. If he throws another fit, give another consequence.