Give bidders the same roof information and ask each to price the same defined work. Compare the proposed roof assembly and named materials, tear-off and disposal, underlayment or insulation, flashings, penetrations, drainage, and allowances for hidden deck damage. The bid should also say how occupied-building access, protection, weather exposure and cleanup will be handled. A low total can reflect an excluded item rather than a saving.
Read the exclusions, change-order process, schedule, payment stages, and separate workmanship and product warranty terms side by side. Request current insurance and WorkSafeBC documentation for project review. If bids use different systems or assumptions, ask for a revised common scope before choosing. Canyon's roofing service page describes the roof and waterproofing work it can scope for a strata property.