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Define the building work
Specify the foundation, opening into the house, structure, roof and frames. Identify any known access restrictions and changes to existing services. A survey may be needed before the scope can be priced reliably.
Agree the finish
Distinguish a shell-only extension from a room with insulation, electrics, heating, plastering, flooring and decoration. Record which items you will arrange yourself.
Compare equivalent offers
Use the same drawings, dimensions and materials. Check provisional sums, exclusions, VAT, disposal and site access. A lower total can reflect less included work rather than a cheaper equivalent solution.
Plan changes and completion
Agree how decisions and additional work will be approved, the expected sequence and what handover includes. Keep the accepted quotation and later changes together as the project record.