Yes...it's hard but not impossible to find furniture made of something else, but if you're using UTH, it's also not recommended for use on metal shelving of any kind.
Wood furniture will add "insulation" to the floor of the cage...meaning heat from UTH goes upward into the cage. As already mentioned, I use some other materials
to help protect the wood also, such as a couple thin ceramic tiles (thick tiles won't fit under the glass with an air gap, and you don't want the glass resting ON them)
A glass tank is designed for & should be resting on the outer framework; I use rubber weatherstripping on the bottom edges & allow a couple air gaps that also allows
the cord (to UTH) to go under tank without the tank sitting ON the cord, which will damage it in time. The weatherstripping also adds safety- the tank won't slide easily.