I'm in the process of signing the contract for a 16x32 free form vinyl pool. They have the depths as 3.5'(3'of water) to 6' (5.5'of water), I would like to change the depth to 4' shallow (3.5' water) and 5.5' (5' of water ). Should this add any cost? Does this change the kit the builder orders since the walls will be taller in shallow end? I'm 5'11 and think that 5.5' of water would be just at the point where it would be at my nose or mouth , I feel 5' would be better. Any opinions? Thanks