Business Registration Certificate
Make sure the contracting party on the contract matches the real owner on the business registration.

All required work items are listed

Start and completion dates specified

Exact material types for each work item

Total project cost and payment method (including VAT)

Issuance of tax invoice

Warranty/defect repair period specified

Terms for contract cancellation and penalties

Two original copies of the contract prepared

Signature or seal of the contractor’s representative

The contractor uses the estimate details to draft the contract, which is their promise to fulfill those terms.
In turn, you agree to pay the total amount upon completion.
Be wary of firms that only provide an estimate and promise to do the work cheaply without a formal contract—this can lead to legal issues later.