Build A Koi Pond

I Have A Koi Pond At The Moment Which Is About 8 Feet By 8 Feet But Is Only 2 Feet Deep. I Want To Build A Pond That Is 16 Feet By 8 Feet And 5 Feet Deep. It All Has To Be Above Ground As I Canot Dig Down.any Ideas.what Do I Build The Walls Of,if I Use Concrete Blocks How Do I Seal The Inside Walls. All Help Will Be Appreciated