Start with the reason this software should exist, not a list of screens. What kind of user will use it day to day, with what frequency, and how is the job done today? An experienced team who knows what you are trying to achieve can propose an alternative that costs less; someone handed only a feature list will price the list as written.
Set out the scope as short scenarios: a walk through each important path. Equally important, list what you are not building. An explicit list of exclusions prevents more argument at delivery time than almost anything else in the document. Also mark which items are decided and which are still open — honest teams price those differently, and pretending everything is fixed helps nobody.
Write down the hard constraints. The list covers systems you must integrate with, the data you have and where it lives, compliance requirements, expected load, supported browsers or devices and any technology stack for web apps you are committed to. If a deadline is real, say why: an experienced team can often resequence the work to meet it, but not if the date is a secret.
Say what completion means feature by feature. Clear acceptance criteria do not require formal language: a plain-language note describing what a user should be able to do will do. This one section compresses acceptance testing dramatically and removes the usual argument at handover.
One last thing, state what you want ai in software outsourcing the response. Require a breakdown by feature or module, the assumptions behind each number, the risks the team sees and an optimistic and a pessimistic figure. Treat a wide range as information, not evasion: it usually points to exactly which requirement is unclear. From there tighten that section and ask again — the second estimate tends to be far closer to reality.
