Nadine, I do not take the outside and yes I do stack them. I usually build a stand out of 2x4s that will support their weight. The stands are usually no more than 18 inches high that way when i do stack a second cage on top it isnt too high to reach into. I have stacked them three high with just a 4x4 to keep the bottom cage off the floor. But thats probably taller than most would like for the third one unless they want a step stool to reach into them. Im almost done with a stand too. I will take a pic of it and the cage on top of it when I get it done.
Like someone else said, I have never been a fan of having chickens on wire personally. Especially for a breeding pen. You want your birds to feel comfortable and having them on wire is anything but. Yes its easier for you because you never have to clean. The cages I have built are that hard to clean either. It takes probably about 3 to 4 minutes most to clean one out and put new shavings in and you are good to go. In my experience chickens raised on wire just dont seem to do as well. Hence I have always put plywood bottoms on my cages.
Building them out of pressure treated and pvc coated wire might be the only way to make them better BUT that wouldnt be so cheap.
I bought 15/32 plywood then had them cut it twice for me to give me three panels of 3x4,3x4 and 2x4. The sheet was only $13. The 2x2s were $1.05 a piece, I used 5. The wire is 1x2 on the sides and is 2x4 on the top.
I think I have built somewhere around 30 of these over the years and the current design is the latest attempt to improve the ease of use and durability.
I made sure the door was big enough for me to go thru to reach in to every part of the cage also. Wire doors are economical and easy but I think the current door is more functional.