Begin with the problem you are solving, not a list of screens. Which people will use this, how often, and what does the process look like without it? An estimator who grasps the purpose often proposes an alternative that costs less; one who only sees a list of screens prices the list as written.
Describe the scope as user stories or scenarios: what the user does and what the system does in response. Every bit as useful, list what is out of scope. A written out-of-scope list prevents more disagreement at delivery time than the rest of the brief combined. Indicate as well which decisions are settled and which are still open — the difference changes the price, and concealing the open questions helps nobody.
Write down the hard constraints. The list covers the platforms and gpt integration services involved, the data you have and where it lives, compliance requirements, expected load, supported browsers or devices and stacks you cannot change. If a deadline is real, say why: a team is usually able to resequence the work to protect it, but only if they know it exists.
Write down what done means for each item. Acceptance criteria do not need special syntax: a short list describing the expected behaviour is sufficient. That one addition reduces the review at the end by a surprising margin and eliminates the usual argument at handover.
To close, state what you want in the response. Request a task-level breakdown, a written list of assumptions, flutter app development company the main risks and a low number and a high number. Take a broad range as a signal about the brief: it consulting services usually points to the part of the brief that needs work. Then rewrite that part and request a revised number — the second estimate will be much more reliable.