I love outdoor cages because there are no dropping trays. (At least, mine don't have them.) I shovel out from under them once a month or so, as the weather permits. Unfortunately, one also has to deal with heat, cold, and precipitation as well. When I see droppings and fuzz starting to build up on the floor wire, and it doesn't take long at all, it is time to blast it off. I've tried many things, like torches and wire brushes, and the best combination I have found follows:
First, I remove the rabbits from the cages. I know that seems, obvious, but you'd be surprised at stories I've heard... Then, I bring out my electric Karcher K 3.98 power washer and blast away. It has a wand that sends an oscillating spray which rips pretty much everything off the wire. I let it dry in the sun, then I take my spray bottle full of pure white vinegar and spray the wire with it and let it sit about 5 minutes, then I hit it again with the power washer. The vinegar dissolves the calcium and mineral buildup from the rabbits' urine, preventing more fiber buildup. I then take a spray bottle with generic Listerine and spray again, then replace the bunns when it is dry.
Meanwhile, after I shovel out the manure under the cage, I dust the ground liberally with hydrated lime. As manure builds up, if the weather is warm, I sprinkle Stall Dry (diatomaeceous earth and clay) over the manure to keep flies from hatching. It really works!
That's how I control buildup, odor, and flies on my outdoor cages. I'll soon post about my few indoor cages, with which I use a very similar regimen, with one notable exception.