On my current build (24" diametric CC ) I installed the front serving rack just under the bottom door flange, the main cooking grate ( grates will be stainless steel round stock) will sit level with bottom lip of door opening. If I'm doing a whole pig or big cuts of meat like butts or brisket, when a sheet pan is placed on the serving rack it will be level with the cooking grate and the meat can be slid from the pan right onto the main cooking grate. I laid it out so that the lip of the large aluminum pans I have actually but right up to the lip on the door opening so that there is no gap.
The top cooking grate ( I will only use two levels on this size dia ) will sit halfway up from the bottom rack. The back of the rack will be hinged at the back wall of the CC, the top rack will now be able to have the front lowered down to cooking grate level for better access to clean it , and that will be the removal position as well, ...or sit lever for the cooking position, or tilted upward with the front of the rack held up against the top of the CC. In the last position , with the rack pushed up against the rear wall of the CC and out of the way, this will give me room for cooking large items like turkey's, etc. with out having to remove the rack from the CC and finding a place to store it. At any time during a cooking cycle, when top rack is needed, it can be tilted down to cooking position , it will already be clean and preheated because it never left the CC .
I'm building this cooker for me, and two racks with the ability to add rib racks to either cooking rack is all the cooking area I need from this one, ...
But, if I was building a larger dia cooker for someone that needed more available cooking area, my thoughts are that by utilizing the stainless round stock instead of 3/4 #9 , the twin racks could be built with inner racks ( think of how a weaving loom opens up ) so that each rack could turn into two racks by lift up the inner rack. Of coarse, you would loose 5 or 6 inches in depth on the inner racks, but shouldn't be that big of deal. Then let's say your cooking a crap load of chicken, it's done and now needs to be placed in pans and kept warm, ...you could just reach in, pull the inner racks forward and the would drop back down to being level with the two main racks and you have room to place your pans back in the cooker!
Just thinking outside the box, and keeping everything inside the CC.