All I use is plain vegetable oil with a few drops of tea tree oil mixed in, but not too much! Its too aromatic to put much, but it's antibacterial and antifungal and deters bugs, so I put it in. I sand the roosts smooth, rub the oil in with a rag, then allow it to soak in all day on a hot day before they go to roost, so they aren't too slippery. Some may slip a bit that first night, but after that, it's fine. It does help so much to keep runny poop from soaking into the boards and makes it easier to clean.
