Picture
This is what we started with for our rabbits.  Some designs were based off a setup were we had picked up from "free" cages and a couple of rabbits.  The cages were all wood frame with chicken wire on the sides and hardware cloth on the bottom.  Wow, I now know how wrong that was.  Newborn kits can fit through the chicken wire.  Hardware cloth is bad more a number of reasons: hard on the rabbits feet and poop doesn't fit through well at all.  The wood is hard to clean and when it gets soaked with urine and feces, is can harbor disease.  We dodged the bullet on all this.  No sore hocks, no diseases, and we stayed on top of the poop piling up and cleaning the cages.  But we did have 2 occasions where new kits got through the wire and 1 occasion where a corner got wiggled bigger and 4 week old kits were free in the garden.  The gutters were a great start but built up quicker than we liked and would overflow if we moved too much out at one time.  2 tiers seemed like a great use of space but there were problems with that.   Last probelm was location.  On the outer edge of our garden seemed convenient, but with it being right by our driveway we got dust (rabbits have sensitive respiratory systems, so not the best idea).  It is also we found the hottest location in the summer and coldest location in the winter.  Rabbits like to be around 50 degrees.  They do much better in the cold, and can suffer and possibly die in anything above 85-90, without doing things to keep them cooler. 

Picture
Close up of our gutter and poop system. The angle/grade is not enough and the gutter is too small for the number of rabbits we had. Not a bad first go but as you will see it is way better.
IMPROVEMENTS: 
I have become the rabbitries main cage builder and all of our rabbits are in hanging wire cages.  We have increased our cages to 30 x 24 and 36 x 24.  We will have an outside area (still in the works), that will be mainly for grow outs.  We will have a few 24 x 24 for the ones that can't seem to get along well with others and a 48 x 24.  Seems like you can never have enough cages, right.  Jess has re-purposed old metal plumbing pipes to hang the cages from.  It works great so far.

As you can see we have opted for the single tier system.  Our grade below the cages is much steeper helping the poop go down to a much larger gutter.  This also helps keep the fumes further away from the rabbits, which in turn keeps their lungs healthier.  So if in theory we take a vacation, we can be gone for at least 1 week and not worry about rabbits sitting in poop.  Yeah.