Trev1

I am planning to build a free standing garage out of 150mm thick concrete blocks. 6m x 5m x 2.7m floor to bottom of room. Intend to insulate and render the inside of the garage with 100mm insulation. My question is do I need to use piers when using 150mm concrete blocks ? What are the benefits and drawbacks to using 100mm concrete blocks with piers instead of 150mm concrete blocks? Thanks .