Begin with the business problem, not a feature list. Who will use the system, with what frequency, and how is the job done today? An estimator who grasps the purpose often proposes an alternative that costs less; a team that receives only the requirements as given can only price exactly what you asked for.
Describe the scope as user stories or scenarios: what the user does and what the system does in response. Just as important, write down what is out of scope. A written out-of-scope list saves more friction during acceptance than almost anything else in the document. Mark too which parts are firm and which may still change — honest teams price those differently, and pretending everything is fixed helps nobody.
Set out your constraints. The list covers systems you must integrate with, existing databases and their quality, compliance requirements, traffic expectations, which devices matter 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.
Define what done means for the important items. Clear acceptance criteria do not need any formal notation: web development company moscow a short paragraph stating what must be true when the feature works will do. That one addition compresses acceptance testing by a surprising margin and closes off the most common source of disputes.
One last thing, ask for a specific format. Require a task-level breakdown, the assumptions used, whatever the team considers risky and software development hourly rate an optimistic and a pessimistic figure. Take a broad range as a signal about the brief: it usually points to the part of the brief that needs work. At that point tighten that section and ask again — the second estimate tends to be far closer to reality.