I found this from the 8 Habits of Awesome UX Designers, “It’s easy to conceptualize an app or piece of software in terms of volume of screens, but looking deeper is integral to the success of any product” being a very true statement.
Many times, well almost all the time as a freelance design firm, I would get clients simply wanting me to give them a quote only on a number of set screens. Of course I would have to do this in order to get the project, but do explain that there could be additional screens needed once we further explore the project and to achieve your main end goal.
Many clients seem to think that having a set number of screens for a website or application will solve the project they had set from the start. Many times this is on not the case and it will vary from client to client, but also from the type of industry or device that we’re building it for from the start.
If you’re truly hiring a user-experience (UX) and user-interface (UI) designer and you want to have the very best possible results, simply give some additional room if needed when the designer is fully immersed within your project as they will have additional perspective that you may not have seen or thought of yet that can help make your project, product, or service a success.