i find that cabbage and brussel sprouts benefit from a minute of boiling..
it reduces gas.
and makes it tender..
but it is also important to drain them well after the boiling..
I've never roasted cabbage but have roasted a lot of Brussel Sprouts. LOL so much that I have grown tired of roasting them and am back to steaming or just plain boiling them.
Edit:
If I am steaming my vegies, as Sweetbun, has suggested, I add beef/chicken/vegetable paste or a cube to the water. Save the water for a soup or gravy, etc.
But most importantly I slather butter all over the vegies to serve!