They're is a possibility that we can build walls in HW. Well, if we can, why not take that to the next level. Spend large sums of money to soup up your walls, each level the walls will get thicker, until a rampart is formed and you have the option to build a staircase.
Now, you're probably going to hate this, and don't insult it if you do, but take the above concept to the next level. Build grav lifts or spiral ramps to get to a second, and potentially third level on your walls. Pretty outrageous, but it will look insanely sweet.
P.S- Don't flame, this was a suggestion, I'm just trying to help out, answer in a polite and civilized fashion.
Just give me some suggestions or ask any questions if you're confused.
More intense debating
http://www.halowars.com/forums/thread/226003.aspx