Double-tier indoor cages?

Ive seen some of these around but they always look quite unsteady. Does anyone have one and have any opinion? They seem to be a fairly easy way of increasing space. No pet shops around here sell any, though.

But I reckon with my current setup (Cage with pen attached) a double-tier thing would be pretty good, then they'd get 2x the cage space plus the pen space...

Those cube things everyone uses won't be any good for me coz really I need a tray like in a cage, because my lot have a pretty sporadic approach to litter-training...

I've never seen them but ours is a large dog cage with an upstairs made with really thick wood with dowels drilled into to fit thru the gaps of the cage, which is fitted to half of the upstairs (which has a piece fitted so that they can't fall off and a 3/4 long shelf which is about a foot wide which they love to lay on which is half way to help them jump upstairs.