Different quantities can describe different jobs
Two roof quotations can use different square-metre figures without either being a simple arithmetic error. One may count the accessible horizontal area, another may include upstands, while a third may exclude a section behind equipment until it can be inspected. Before comparing a unit price, ask what the quantity represents. A written measurement basis gives the owner a way to understand the scope and query differences without pretending to carry out a technical survey.
Begin with a location drawing that everyone can recognise. It can be a marked plan supplied for the quotation exercise, with each roof section named consistently. The drawing should identify its origin and any unverified dimensions. Avoid presenting a rough owner sketch as an accurate measured survey. Bidders can then explain whether they checked the dimensions, relied on supplied information or priced a provisional quantity subject to measurement before work.
Keep area and details in separate lines
Ask each quotation to distinguish the main roof area from details that the contractor prices differently. Depending on the proposed work, those details might include junctions, penetrations, terminations or access-related work. The owner does not need to prescribe a construction method. The purpose is to find out whether a quoted square-metre rate covers those items or whether they appear elsewhere in the price. An apparently low rate can be a poor comparison when the significant details remain unpriced.
Use the same location names in the schedule and the contractor's drawing. A line described as upper roof should identify whether it includes the small roof over a stairwell. If the contractor uses a different measurement convention, request a note explaining it. Do not force unlike systems into one invented rate by dividing every cost by the largest area. A complete fixed-price proposal and a remeasurable schedule answer different commercial questions and should be labelled accordingly.
A worked comparison of two proposals
Consider a fictional villa with an owner-supplied sketch showing roof A and a smaller roof B. Bidder One lists 120 square metres of main roof and a separate allowance for details. Bidder Two lists 145 square metres with no drawing. These numbers are illustrative and do not describe a Waterproofed project. The owner should ask which sections and surfaces each figure includes before deciding that one bidder has measured incorrectly or that the other is offering better value.
Suppose Bidder Two confirms that its figure combines horizontal surfaces and parapet faces, while Bidder One has listed parapet treatment separately. The owner can now compare the proposed treatment of the same locations. If roof B is absent from either schedule, that is a scope question requiring a written answer. Simply replacing both quantities with their average would hide the omission. The useful outcome is a reconciled location list, not a visually tidy spreadsheet with unsupported numbers.
Agree the treatment of provisional measurements
Some quantities cannot be confirmed without an agreed opening, access arrangement or removal stage. Label them provisional and ask how the eventual quantity will be established. The proposal should explain who measures, which record supports the measurement and how the agreed rate or price adjustment applies. Ask whether there is an approval point before additional work proceeds. That keeps an estimate from silently becoming an open-ended instruction when the contractor encounters a larger area.
Where the price is fixed for a defined scope, ask what would count as a genuine scope change. A contractor should not need to invent extra square metres to explain work that was already included. Equally, an owner should not assume that an unexamined neighbouring roof was covered because the original email used the word roof. Record inclusions by location, retain the agreed drawing and make later changes traceable to a revised description.
Compare omissions before negotiating the total
Build a comparison table containing location, measured basis, proposed work, exclusions and price treatment. Leave a blank where a bidder has not answered. A blank is a request for clarification, not a zero-cost inclusion. Ask both bidders the same focused question and retain their replies. If one offers an optional item, keep it outside the base comparison until you decide whether every proposal should include it. This makes negotiations about the actual work rather than an unexplained headline total.
Keep tax treatment visible in the financial summary without guessing which rate applies. Ask the supplier to show the applicable tax separately and clarify whether any quoted total includes it. When the property belongs to a business, send the final agreed commercial documents to the person maintaining its records. Accountly offers a separate accounting enquiry route for that discussion. An accountant's treatment of an invoice does not validate a roof measurement or approve a repair method.
Close the measurement record before starting
Before acceptance, obtain one version of the scope with the drawing and quantity schedule referenced together. Mark superseded sketches clearly so that the site team does not work from an earlier email attachment. If an area remains excluded, state who will decide whether to include it later and what information that decision needs. Keep photographs tied to location names rather than using a folder of anonymous close-ups that nobody can reconcile to the roof.
A useful clarification sheet can have one row for each roof section and a column naming the drawing used. Ask bidders to return corrections against that sheet. If a later site measurement changes a quantity, retain the earlier figure and the reason for revision so the owner can reconcile the difference without reconstructing the original enquiry.
A Waterproofed assessment enquiry can explain that the purpose is to clarify roof scope before comparing repair proposals. For broader refurbishment planning, Renovated is another relevant service enquiry, with its scope confirmed separately. A single agreed location schedule can support both conversations while each contractor remains responsible for its own measurements and proposal. The decision becomes easier when quantities describe the same places and every remaining assumption has an owner.