Begin with the reason this retail software development should exist, not a list of screens. Which people will use the system, how many times a day, and what does the process look like without it? A vendor who grasps the purpose often proposes an alternative that costs less; someone handed only a list of screens can only price the list as written.
Set out the scope as user stories or scenarios: who does what, and what happens next. Just as important, write down what the first release deliberately excludes. A written out-of-scope list prevents more friction later than any other single page. Also mark which items are decided and web development company russia which may still change — honest teams price those differently, and concealing the open questions helps no one.
Set out your constraints. This means systems you must integrate with, the data you already hold and its condition, compliance requirements, traffic expectations, supported browsers or devices and top flutter development companies any technology you are committed to. Where a date is genuinely fixed, say why: a good outsourcing dedicated team can often rearrange the plan to protect it, provided they hear about it early.
Define what the word done means for the important items. Acceptance criteria do not require special syntax: a short paragraph describing the expected behaviour will do. That one addition compresses acceptance testing by a surprising margin and closes off most late-stage disagreement.
One last thing, state what you want in the response. Ask for a breakdown by feature or module, a written list of assumptions, the risks the team sees and an optimistic and a pessimistic figure. Read a wide range as useful information rather than evasion: it normally identifies where your description is thin. From there tighten that section and ask for a new estimate — the second estimate tends to be far closer to reality.