First I purchased 2 Critter Nation double units. I decided I wanted a third, and ordered.  When it arrived I installed half of it to one of the first two cages, to make a tripple unit cage.  I then added the remaining unit to the other cage, and cut an access hole to allow access to the third level.  so now i have 2 tripple unit critter nation cages. Sweet!!!.  I am exploring an idea of removing the stands and building a bench style base out of wood, and tall enough for the top of the third story of these things to be nearly kissing the ceiling.