My first cage was from a kit. I wanted to see how one was put together. I quickly decided I didn't like the clips that came with it, so I switched to J-clips. I also had to invert the floor because it was attached (by the manufacturer) inside out. I like for my doors to hinge at the bottom, so that they drop down completely when they're open. I use the finger-loop spring latches from Bass to keep them closed.
I make my cages from wire that I buy in rolls from TSC. I use this for the sides and top:
http://www.tractorsupply.com/fencing/welded-wire-fencing/cage-wire-36-x-25-ft-1-x-2-in--3627241
and I use this for the floors:
http://www.tractorsupply.com/fencing/welded-wire-fencing/cage-wire-30-x-10-ft-1-2-x-1-in--3627209
I use these dropping pans:
http://www.tractorsupply.com/pet-ca...e-plastic-dropping-pan-30-in-x-30-in--2180597
Even if you can't find it in your local TSC, you can order it online and have it shipped to your local TSC for free.
I prefer using J-clips to fasten the wire together. Make sure you have plenty of J-clips, a good pair of J-clip pliers, and gloves (to pad your hands). I order the clips and the pliers from Bass. And, as ladysown mentioned, good wire cutters.
I started out by making the sides all one piece and bending the wire at the corners in order to save wire and J-clips. I've decided I don't like that idea because the cages don't come out quite square.
As for stacking/hanging, I think a lot depends on where your cages will be located and how much space you have. The best thing to do there is to get ideas from the other people here and pick what suits your situation best. Mine are currently in our attached garage, although I hope to have a barn to put them in someday.
Here is my stacking system for my 30"x30" cages. I'll try to get photos that will show how it's put together. I got a lot of my ideas from moonkitten's Web site. I designed a 2-cage system out of 2x4s, 1x2s, and L-brackets. 6' 2x4s form the uprights in the corners, with horizontal 31" 2x4s across the sides, at the top, center, and bottom. I have L-brackets attached to those to hold the cages. I have horizontal 31" 2x4s across the front and back, with three slats of 31" 1x2s (front to back) to hold the dropping pans. The whole thing is braced on the sides and back with 8' 1x2s attached diagonally. It's all put together with screws (nails are NOT a good idea--they'll work loose.) Lesson learned from this project: make your stacking system just a little bigger than your cage dimensions, or you might find it too tight for your cages to fit.
(Remember my not-quite-square cages?) :evil: Still, I do like the design, and three more of these are on my DH's honey-do list (he's better at the actual construction stuff than I am).
