Why two builder quotes for the same house differ.

A set of drawings is not a scope. It shows where the walls go and what the rooms are; it does not say which tapware, which tiles, which windows, whether the driveway is in, whether the site works are allowed for, what happens if the soil is worse than expected, or how long the builder expects to be on site. Every builder fills those gaps with their own assumptions, and the price that comes back is the price of their assumptions as much as of your house.

Inclusions and exclusions are the first reason. One quote includes the driveway, the fencing, the landscaping and the connection to the services; the other stops at the back door. One allows for the site works the block will need; the other carries a provisional sum and will charge the difference. Neither is wrong, but they are not comparable until you read the fine print, and most people compare the totals.

Product allowances are the second. Where the drawings do not name a product, a builder allows a sum for it: so much for the tiles, so much for the kitchen, so much for the tapware. A low allowance makes a low quote, and the difference arrives later as a variation when you choose the products you actually want. Two quotes with different allowances are quoting different houses.

Quantities are the third, and the least visible. Each builder, or each builder's estimator, measures the drawings themselves. Small differences in how the wall areas, the roof, the openings and the concrete are taken off become real differences in the total, and nobody outside the builder's office can see which measurement is right.

Margin and preliminaries are the fourth. A builder who is busy prices high; a builder who needs the work prices tight; both carry preliminaries for supervision, site set-up and time on site that differ with how long they think the job will take. These are legitimate differences, and they are the ones worth comparing, but you can only see them once everything else is held equal.

The remedy is to take the scope out of the builders' hands and give them the same one. Decide the products, or at least the finish level, before anyone prices. Measure the quantities once, with the working shown, so every builder prices the same square metres of wall and the same number of doors. List what is included and what is excluded so that no quote can quietly drop the driveway. Then the differences that remain are the builder's own: their rates, their programme, their margin, their qualifications, which is exactly what you want to compare.

That is how a builder round works on Modern GBQ. You approve a Design or Detailed estimate, and every invited builder receives that scope: every included line with its quantity and labour hours, the excluded lines listed separately, and your rates and totals only if you choose to share them. Each builder accepts, sends a revised proposal, requests a discussion or declines, with written notes on programme and qualifications. You read the responses blind, as Builder A, B and C, before any name is shown. Then you choose who to talk to, and the contract is between you and that builder directly.

Two quotes will still differ. But they will differ for reasons you can see.