I built a base for my cage and I think it is very sturdy that way. If you look at my pics you can see what I mean. I have seen some cages built on the floor or on tables or what not. But, I the way I did it there is a lot of stability and a lot of storage space.
Here are a few pics, so you can see what I mean.
First I built the base. Then I built the sides. Eventually I will build on to it and make more levels.