I want to add a second level for my girls and wanted to know how to support the upper level so it's not sagging? I know I can use zip ties so it doesn't fall down but I want to make sure there isn't sagging?
Also, how could I make my cage like this? So cool!!
You mean the top of the cage? Turn it over like the middle level.
Or, you can get 2x2's at a home improvement store and run them lengthwise down the middle. They're actually not 2x2 -- that's the nominal size -- so they should fit.
They're running something under the floor of each level (such as the 2x2's I mentioned, or a long rod of some kind), or they're using closet shelving for the floors.