When roasting cabbage, you want the same sweet nuttiness from caramelization and browning that you achieve with roasted broccoli. But, given the way cabbage is shaped, I've found that, as with cauliflower, the best way to prep it for roasting is to cut it into thick wedges through the core, so the leaves hold together.
Split your cabbage head through the core into six to eight wedges; toss with oil; season; and roast at 500°F (260°C) until the cabbage is browned and tender, flipping once during cooking.
The Full Story
As with other brassicas, high heat is what you're after here in order to get the most flavor out of cabbage. Cutting the head up into fat wedges helps build up a nice contrast between deeply browned exterior and tender, meaty interior. The cabbage wedges are hefty enough that when you cut into them, it's almost like cutting into a big vegetable steak.