I am using chemical plants and refineries. You have to make sure you are producing required resources and that you are transporting the resources from the factories where they are produced to the warehouse and then from the warehouse to the factories where they are needed.

Usually you need to transport Oil to the refinery to produce petroleum and then transport the petroleum to the chemical factory along with any other resources you may need.

You also have to transport the finished product to the warehouse.

Hope this helps.