Hi and welcome Adam. I have my cage in a corner and I would very rarely find any poo on the walls and never pee, although mine never get inside the wheel merely jump on top of it to make it spin. From my experience I would probably get rid of the ramps mate so you could get a good cutting of a tree in. My chipies would never run up those ramp, but jump to the top of the cage via the tree and wire cage. You could have the ledges on one side to leave them with freedom to have a burst of speed. The tree and levels will allow you suspend little treats and game type things, and its a more natural way to get to their home. Mine have just loved eating the stuffing out of mr monkey from the pound shop. Having a nice hammock for them to lounge if they fancy a siesta is appreciated, especially if one become dominant. They also like tubing, I got some of that bendy type ducting from b&q £5. It is metal, but just make sure you round the edges enough so u can rub finger around. You get plenty of length and its easy to form and clean. Try and not make everything fixed so you can change things about to keep them interested. If you don't want dirty walls don't get soil from what I've seen, although mine are not interested in soil at all. I use a sawdust try to let them know where to pee & poo, and have the bottom done with hay and the ledges done with carpet just to mix it up. The carpet actually looks well, it is brown mind. Think that's enough for now, happy building.