[Otaku]

It really depends on whether your hamster is a chewer or not. My boy isn't so I have been able to use plywood for shelves coated with Ronseal Garden Paint, a pet safe paint.

If your hamster does enjoy nibbling wood then you can't use treated woods or those with adhesives (the latter eliminating plywood from your options) BUT I have seen lots of DIY projects that have used the IKEA Knuff magazine holders to create shelves and/or platforms.

So, I think a lot of people would recommend untreated pine but I have seen a lot of others use plywood (the Knuff).

I think get to know your tiny Tim a bit more and learn if he can be trusted with plywood or not, but regardless ensure he has plenty of chew toys (i.e. Whimzees) to keep him happy and healthy. xo