I just finished a C&C 4 level cage for my 3 rats last night. I was able to find purple wire mesh grids on clearance at Shopko and bought 2 boxes. The holes in the corners I covered with binder clips so my girls can't escape. And my husband used just a straight stiff wire for holding the doors shut - it's very simple, effective and easy to use. The doors are hinged on with more wire.
I had one rat (her cagemate died), then I adopted two a few days ago. The rats seem to enjoy all the stuff to do. I'll be adding a few more items to the cage soon. I found some bird shelves that will work perfectly. My rats also like the "hidey hut" in blue at the top of the cage. It's triangle shaped and has a firm base on the bottom. It's for birds but makes a great napping place for a rat.
I'm sure I'll find improvements to make (like making the main floor more clean looking), but I was just excited to show it off.
