That's cute!
Actually though, pouches can be, and are often hung along the sides of the cage. They don't have to be hung from the roof, though can be. Some hang them on the door of the cage.
I personally keep mine hung in the corner. I've had hung them around in different ways over the years, but I find they're less disturbed in the morning after they go to bed and I want to take out food dishes and do daily tidying up. I can access them easily in the front left (facing) corner if I want or need to.
Even if you wanted to, a braided fleece vine that is hung taught enough could be used to hang a pouch from, if you can't find a properly fitted shelf.
The main concerns about a cage are: bar spacing, size of cage, sturdiness, and style and size of the door(s).