If the planet spins, it is hollow because centrifugal force will force heavy elements away from the center while gravity will push towards the center. The balance generated between centrifugal force and gravity is where most heavy elements exist and also where we all walk.
What Earth may actually look like inside:
Science and history Books must read:
https://www.amazon.com/Hollow-Planets-Feasibility-Possible-Worlds/dp/099134975X
http://www.sacred-texts.com/earth/jei/index.htm
https://www.amazon.com/Ultimate-Reality-Vol-1-2/dp/0787313408
https://archive.org/details/etidorhpaorend00lloy
https://archive.org/details/smokygodorvoyage00emer
https://www.amazon.com/Passport-eternity-Laurence-W-Foreman/dp/B0006CKPPW
Japanese scientists on Hollow earth: http://zao.jp/index.php?blog=12&p=340&more=1&c=1&tb=1&pb=1