Start with the business problem, not a list of screens. Which people will use it day to day, angular for enterprise applications how often, and software development pricing what happens today? An estimator who understands the goal can propose a simpler way to reach it; one who only sees the requirements as given will price the list as written.
Describe the scope as short scenarios: who does what, and what happens next. Equally important, list what you are not building. An explicit exclusion list saves more disagreement during acceptance than the rest of the brief combined. Also mark which items are decided and which are still open — estimators price uncertainty, and hiding it helps nobody.
Write down the hard constraints. These include systems you must integrate with, the data you have and where it lives, regulatory obligations, traffic expectations, supported browsers or devices and any technology you are committed to. Where a date is genuinely fixed, say what depends on it: a good team is usually able to resequence the work to hit it, but only if they know it exists.
Define what completion means feature by feature. Acceptance criteria need not use formal language: a short paragraph stating what must be true when the feature works is enough. That one addition shortens the review at the end by a surprising margin and closes off the most common source of disputes.
To close, say what you expect back. Ask for a task-level breakdown, the assumptions used, the main risks and a low number and a high number. Take a broad range as useful information rather than evasion: difference between flutter and react native it usually points to the part of the brief that needs work. From there tighten that section and ask again — the revised figure is far closer to reality.