as the client, i would always split the project into 2 parts - a functional spec and a technical spec. my job was to interpret and write the func spec as a kind

as the client, i would always split the project into 2 parts - a functional spec and a technical spec. my job was to interpret and write the func spec as a kind of pseudo-code version of what i thought could be built. then i would commission a fixed price job of interpreting the func spec and re-writing it as a technical spec ie, click a button and take the user to a summary of xyz turns into a bit of SQL. the tech spec must be written so that any programmer could use it to understand what needed to be done. then I'd ask for a fixed price quote to deliver on the assumption that i could get multiple quotes if needed. the benefit is that my coder who wrote the tech spec should be very comfortable with what is needed and i get to sell a lower risk $$ to my managers.