Begin with the business problem, not a list of screens. Who will use the system, with what frequency, and how is the job done today? An estimator who understands the goal often proposes an alternative that costs less; someone handed only the requirements as given prices exactly what you asked for.
Set out the scope as concrete flows: what the user does and what the system does in response. Just as important, list what is out of scope. A written out-of-scope list prevents more argument later than almost anything else enterprise software development in java the document. Indicate as well which decisions are settled and which are still open — estimators price uncertainty, 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, traffic expectations, supported browsers or devices and stacks you cannot change. If a deadline is real, say why: a good team will often cut the right scope to meet it, but only if they know it outsourcing eastern europe exists.
Write down what completion means for each item. Acceptance criteria do not need formal language: a short paragraph describing the expected behaviour is enough. That one addition shortens acceptance testing by a surprising margin and eliminates the usual argument at handover.
To close, state what you want in the response. Ask for an itemised estimate, a written list of assumptions, the main risks and a range rather than a single figure. Treat a wide range as information, not evasion: it normally identifies the part of the brief that needs work. Then clarify that area and ask again — the second estimate tends to be far closer to reality.