I made a couple boxes for the piggies out of wood. They are 2 sided so they can pass through on either end. They're very rigid so they can climb on top and lay around too. I use one as the ramp base and the ramp itself is made out of the same wood. They're able to chew on them too. I put the other box to the side of the ramp/front of the cage so that if Kevin needs to escape Gary he can safely. Kevin loves the second story, he spends a lot of time up there, Gary loves the main level. Gary chases Kevin a lot and Kevin often ends up on top of one of the boxes so that drove me to build the second story and give both piggies more space and freedom to choose to be with one another or more alone time. The green full panel on the second story keeps the roof from sagging.