Comment by mytailorisrich

This should only be a first phase of the design and should be high level and not a commitment. Then you quickly move on to iterate on this by writing working code, this is also part of the design.

Having an initial design approved and set in stone, and then a purely implementation phase is very waterfall and very rarely works well. Even just "pitfalls and pros & cons" are hard to get right because what you thought was needed or would be a problem may well turn out differently when you get hands-on and have actual data in the form of working code.