I'm sure other people will respond to say how bad wood chips are so I won't
detail it... Try Linoleum.  It's cheap; get scraps or samples-- a local
builders supply sellls them here in VT for a buck.  It's easy to clean, and
the messiness factor really convinces the fuzzies to use the cage's litter
box.
 
once again,
Elfyr & Finnegan
[Posted in FML issue 1238]