Ask a previous client whether the team kept to agreed dates, left the site tidy and came back to deal with defects. Give the contractor one tricky detail from your drawings and ask how they would build it. A useful answer refers to the drawing and the manufacturer’s instructions. An assurance that they always do it the same way is little help when your roof or wall has an unusual build-up.

List the tasks and the finished elements you expect. For a roof, distinguish the structure, underlay, insulation, covering, flashings and drainage. Agree who prepares openings and service penetrations. If the handover between trades is unclear, each contractor may assume someone else is responsible for a difficult junction.

Include deliveries, unloading, scaffolding, lifting equipment and waste removal. Specify how the building will be protected overnight and during breaks. These tasks cost money and affect how the site runs. With a full description, you can compare quotations for the same work and see what each price actually buys.

Appoint one person to communicate decisions as the job progresses. When several people give instructions independently, changes can conflict. A short written confirmation should state what will change and whether the price or timing is affected. Both parties then have the same record to work from.

Record the material specifications in the design and cost estimate. For profiled sheet, note the profile, sheet thickness, coating and effective cover dimensions. For insulation, record its intended use, thermal conductivity (λ), thickness and facing. A generic product name leaves room for a substitute that may need a different fixing method or be unsuitable for the planned use.

Agree how alternatives must be proposed before they are bought. Price and short-term availability are only part of the decision. Review the implications with the person responsible for the design. Keep delivery records and product documents so you can establish exactly what was installed and why.

Before fixing dates, check when the site will be ready for each trade. Roof covering can begin only once the structure has been accepted and the materials have arrived. Some tasks also depend on the weather. Set out the stages, which ones depend on others, and how delays will be reported. A single completion date does little to coordinate several teams.

Ask how many people will be on site and whether the contractor will be working on other projects at the same time. Agree what needs to be in place to restart after a break. Schedule deliveries of long sheets only when the site is ready for unloading. Even high-grade material can be damaged in makeshift storage before it is installed.

Arrange inspections before fixings, insulation, seals and roof layers disappear from view. Take a photograph that identifies where each detail sits, as well as a close-up. Link the photographs to a drawing and record the date of that stage so the detail can be found again.

Stage payments can be linked to the agreed work and its acceptance. Record each defect with its location, the agreed remedy and a deadline. Verbal agreements are harder to reconstruct later. A roof inspection needs to cover more than its appearance from ground level: some of the most important work cannot be seen from the street.

The contractor, designer and site manager have different roles. Hiring an experienced team does not by itself settle the client’s responsibilities for organising the build. Before work begins, establish which procedure applies, who will take on the technical roles and how documents will be handed over. The formalities depend on the proposed works.

The contract should identify the parties, scope, price, dates, inspections and procedure for defects. Specify how materials will be protected and who is responsible for damage. Review any extensive or unusual terms before signing. Clear agreements make everyday cooperation easier and reduce disputes while work is under way.