"We're all too humble," he said, attacking builders for promising short work time-frames.
Sewell said he did not want to commission a new building which went up fast but suffered defects.
A builder who gave an 18-month time-frame versus one giving a two-year build period left him wondering "what's the 18-month guy missed out?".
Honesty was critical, he said.
Sewell criticised main contractors for blaming subcontractors, saying as a client, he had only one contract and that was with the main contractor and he did not want to hear of issues with subcontractors.
Richard Aitken, Beca Group executive chairman, encouraged a more collaborative approach between developers, builders, consultants and owners: if they met at the outset and formed a team, the outcome was far more successful than a silo or segregated approach.
Sara Fox, project director for Swiss Re's The Gherkin office tower in London, said she would not let a tenant decide on the facade treatment or the core building services.
Roger Blakeley, Auckland Council chief planner, told the builders: "You people hold the key to unlocking the puzzle. We need a huge shift upwards. It needs a quantum shift."