The only problem I see with stacking them is cleaning them out .
I like a coop I can walk in & clean .
We Framed the run with 2x 4 s .Covered with horse fencing ..which eventually became the coop .
Then we were going to make the run bigger ...but instead we added another frame and and fencing on the end of the run
and it became a baby coop ..
For Broody Hens and babies ...But it could be a small breeding pen too ...Each has its own gate