Hmm... there have been many threads on making your own cages and all that stuff, but i cant seem to find them (other than the link below). Some breeder also has directions on their site but I can't find that either. Maybe someone else remembers, or can find it. Styrofoam?
depending on how tall your platform is, you can use a hide or laybox as a step for them to use on the way up or take a thick branch, lean it against the platform and anchor it with a (heavy) hide or lay box. I am doing both with good success.