concrete blocks bricks

After being let down by several structural engineers wondering if anyone on here will be able to help me. I purchased a new house 4 months ago and the garage is my next project. Water has been getting in for several years and it has rotted the existing suspended floor rendering it useless...

Morning I am building a pizza oven outside and will be using bricks on the visible parts and wanted to use concrete blocks round the back and sides which wont be seen. The concrete blocks will still be open to the elements and I have been told that I will need to render them as they cant be...