Start with the outcome, not the price per square meter
Define what you actually want to end up with: a sheltered seasonal terrace, a heated living room, a winter garden, or a restaurant hall. Fix whether you need a foundation, interior finishes, heating, ventilation, and lighting. Words like “premium” and “turnkey” are not a substitute for this list: different proposals can hide very different scopes behind them.
Record three areas instead of one
Ask the contractor to show floor area, facade glazing area, and roof area. Add height, perimeter, and geometry. For example, in our terrace project above a penthouse, the space itself is 100 m² while the glazing area is 300 m². This is a project with construction scheduled for 2027; it should not be presented as a completed build.
Separate the roof, facades, and doors
The estimate needs distinct line items for the frame, profile, insulated glass units, roof, and operable elements. For door assemblies, ask for the system, dimensions, number of leaves, opening method, and hardware package. If a heated glass roof is under consideration, the proposal should clearly define the supply boundaries for controls, connection, and commissioning.
Check what the renderings don't show
For an extension, the foundation and the junction with the existing house matter; for a rooftop, it is the load transfer to the slab, access, and the lifting route. Ask for a separate breakdown of structural reinforcement, sealing, drainage, restoration of finishes, and protection of existing surfaces. Fix who prepares the site and provides access.
Align the design documentation
Clarify the list of sections, input data, number of approvals, and the final document set. Architecture, steel structures, steel detailing, transparent structures, and building services are not the same thing. Not every project requires the same package, so the section names should match your contract rather than a marketing list.
Match responsibilities and timelines
Break out the timelines for design, approvals, fabrication, delivery, and installation. Note dependencies on the client and adjacent contractors: provision of drawings, preparation of the base, permitted work hours, and utility connections. Ask for exclusions from the price to be listed and for the procedure for approving additional work.
Checklist before choosing a contractor
Check the intended use and dimensions; facade and roof areas; IGU makeup; frame and profiles; number of doors; base and junctions; delivery and lifting; heating and ventilation; finishes; design sections; and the handover procedure. Compare the bottom-line figure only after these items have been aligned. For a bespoke terrace, a transparent estimate is more useful than a blanket “all-inclusive” promise.