I don't feel I am the best person to say what you can use , but can give you some pointers what not to use ...
Resinous and aromantic woods are not good for guinea pigs - e.g. , air-dried pine, cedar and eucalyptus.
MDF - as far as I am concerned . MDF is not safe because of the ingredients added to the wood.
Many forum members ( me included ) have structures made of ply wood and kiln dried pine. These woods are not ideal to be chewed , so I advise doing your best to discourage your guineas from chewing them and provide plenty of chew toys too.