We're not normally big fans of keeping a lot of stuff on top of a vehicle. Bikes, kayaks, skis, sure, but not a lot of random heavy gear lashed down. Yet sometimes you just run out of real estate everywhere else on the vehicle, and at that point it's break out the ratchet straps time.
The Yakima MegaWarrior is one of the largest roof racks you can get: 52 inches long by 48 inches wide, spanning the top of our Jeep Wrangler. It's nice that it's so wide, since you can just grab the side of it to support yourself as you're getting stuff in and out. Racks that are narrower require more of a reach to do that.
We installed a set of Kargo Master folding hinge steps (about $80 on Amazon) which we like a lot, and that makes it even easier. Remember that rooftop cargo baskets don't generally hold a lot of weight, in this case just 135 pounds. That's probably due more to the weakness of how it attaches to your vehicle than any inherent limitation in the basket itself, but pay attention anyway. Put your bulky but light stuff up there, like tents, sleeping bags, etc.
If you need more room Yakima sells a 22 inch extension for a stout $139, and a fitted cargo net for an only slightly less stout $49, but again watch the load limit. Yakima does include the clamps with the MegaWarrior, as well as a wind deflector, and we had no problem attaching it to our Thule Aerobars. After a summer of use it's still bombproof, and really convenient for those times when you've got an extra bike or whatever that you just need to get from one side of town to the other. Plus, Jeeps need racks. Just saying.