Build a quote calculator sheet so every price adds up the same

Help me build a quote calculator in Google Sheets.

My trade: [what you do]
How I price: [e.g. day rate, per square metre, per item]
My rates: [give them, or leave blanks]
Materials and markup: [e.g. cost plus 15%]
Extras I sometimes forget: [e.g. waste removal, parking, travel over 10 miles]
VAT: [registered or not]

Ask me up to 3 short questions first if anything important is missing. Wait for my answers.

Then:
1. A sheet layout: job type (dropdown), quantity, labour, materials, each extra (dropdown yes/no), subtotal, VAT if it applies, total.
2. The formulas for each total, in Google Sheets.
3. The dropdown options to set up for job types and extras.
4. A worked test job using made-up quantities so I can check it adds up.
5. A checklist of extras to ask about on every site visit.

Leave my rates blank if I haven't given them, and check VAT rules on GOV.UK rather than stating them. Only use what I've told you, leave blanks for anything I haven't given, and don't invent facts or figures. UK English.

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