yeah, you gave inches and I converted to feet 'cause it made more sense to me... then I noticed a pattern in the measurements between your cage and mine and realized yours converted to grid-lengths pretty precisely, so I took a guess that you were thinking NIC (seemed like too much of a coincidence for all three measurements in inches to be evenly divisible by 14, plus what else is gonna be that big?
).
here's my condo... I have a little built-in shelf for myself on the top row of grids, since they don't need a 3-grid-high ceiling over the landing anyway.
dowels from home depot are 4' long and are a great fit to run along a length of 3 grids - they're gonna be your best friend for keeping shelves from sagging and adding stability to the condo. although... dowels are like $4 at my home depot and for a cage that size you'll need quite a few... I'm thinking 1x1s or something like that might be cheaper and just as effective.
for 3 x 4 x 6... hmm... ok, bear with me here, I'm overdue for sleep, have zero artistic skill and don't have anything like MS paint on my comp so you're getting a crudely drawn, 1-dimensional, not entirely to scale image hand-drawn on a piece of notebook paper and scanned onto my comp. (oh, and now I'm cranky, because my comp has continued its new trend of me not being able to upload anything (ie scanned or from the camera), edit it and get it uploaded to photobucket without my computer's CPU usage maxing out at 100% and refusing to go down until it's had a reboot... and after a reboot, it takes 10 freaking mins for firefox to be functional again.)
ok, to translate my craptastic diagram...
you're looking at the condo head-on; it's four grids wide and three grids deep.
the thicker lines indicate where flooring will go.
the "o"s indicate the ends of dowels/floor supports - they'll run front-to-back. I forgot to put ones in the same rows along the ceiling - you'll want ceiling support as well to prevent sagging.
ll = that floor space is open to allow bunns to move up to the next level
X over two grids indicates that on the front face of the condo, those two panels will open up to function as a door (carabiners work well to clip them shut) - doors only need to be 1 grid high to get good access, but they NEED to be two wide so that your shoulders can fit into the condo. mind you, I have trouble believing this will be effective when the condo is three deep (works great with 2 deep, though)... I'm wondering if you could put doors in the same locations on the back side of the condo without compromising the stability, because I think that would be necessary to clean the entire floor. probably possible if you also use some vertical dowels/supports.
as a note, the trickiest door to manage will be the one on the third floor - it has to be on the bottom half the level instead of the top so that you don't need a ladder to make use of it. this essentially creates four "free-moving" panels in a square, which is the biggest threat to stability with this design since it's a large unsupported space, you have to hold up a floor there and the end of the floor is floating (ie doesn't go all the way across). the best solution would be to only do one open grid/a 1-grid landing so that 2 of 3 rows (length-wise) connect all the way across and to use support beams that are longer than a standard dowel and place them length-wise instead of front-to-back.
looking at the second and third level floors from a bird's eye view, you could have either 9, 10 or 11 of the 12 grid spaces filled in by that level's floor and on the little between-level landings, it could be 3, 2 or 1 grid-space in size, respectively. just depends on whether you want a deeper landing or more floor space on the true levels. if you want to maximize romping-around space, I'd go with 11/1.
as a note, for stability purposes, the ground floor's floor needs to be filled in with grids in a sky-scraper style condo.
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if you want to be practical, I'd recommend going with a 4x2x6. if you want to build the biggest, most bada$$ condo a bunny (or human) could ever dream of having, you could stick with the 4x3x6. practical has it's upsides, but I vote in favor of the obscene mansion just because it would be so **** impressive! if you go with the latter, I'd be happy to consult, help troubleshoot and brain-storm about renovations if something needs improving just so I can be a part of the process! I've taken apart/reassembled my condo a couple times, so I've figured out the best ways to go about building something so big.
honestly, I think the hardest part would be the flooring, unless you've got some tools/know how to work with wood and have or know someone who has a decent-sized pick-up truck or van (ie big enough for full sheets of plywood)... then it really wouldn't be so bad.
regardless of whether you build in moderation or to excess, make SURE you like the location you pick if you live alone, lol. I had to move my condo once to upgrade to a larger tarp (one that could cover my whole living room instead of an 8'x10')... I cut the top 2 grid-heights of the condo off so I could move the top half and bottom half separately, but as a 5'4'' female working alone, it was still a major hassle.
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sorry for the rambling... got excited about designing a dream condo, lol... if anything doesn't make sense, let me know and I can probably clarify it after some sleep.