Open with the business problem, not your preferred technology. Which people will use the system, how often, and what does the process look like without it? A vendor who grasps the purpose often proposes a cheaper route to it; a team that receives only 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. Just as important, list what you are not building. A written out-of-scope list removes more friction at delivery time than almost anything else in the document. Also mark which decisions are settled and which are still open — the difference changes the price, and hiding it only hurts you.

Set out your constraints. The list covers the platforms and custom development vs saas services involved, the data you already hold and its condition, security and compliance rules, expected load, which devices matter and infrastructure that is already decided. Where a date is genuinely fixed, say what depends on it: an experienced team is usually able to cut the right scope to meet it, but only if they know it exists.

Say what done means for the important items. Acceptance criteria do not require any formal notation: a short list stating the expected behaviour will do. That one addition shortens the sign-off process by a surprising margin and removes the most common source of disputes.

Finally, say what you expect back. Request a breakdown by feature or module, a written list of assumptions, the main risks and a range rather than a single figure. Take a broad range as a signal about the brief: .net dedicated teams it tells you exactly which requirement is unclear. At that point clarify that area and ask again — the next version will be much more reliable.