Why you should see a sample
Ask for a sample of the specific glass, not just a photo of someone else's facade. View it from outside and from within, next to your home's materials, under different lighting conditions. In the technical specification, lock in the selected product and its properties, along with the procedure for approving any substitutions.
Daytime reflectivity is not the same as evening opacity
The appearance of reflective glass depends on the balance of interior and exterior light: in daylight, with a darker interior, the reflection is more pronounced, while at night an illuminated room may be visible from outside (Guardian Glass on reflectivity and privacy). For a terrace, sauna, or gym, discuss the evening scenario separately: the placement of lighting, curtains, screens, or another design solution.
Three characteristics instead of a single adjective
Guardian distinguishes reflection, absorption, and light transmission; exterior and interior reflection may also differ (technical explanation from Guardian Glass). Ask the proposal to list the properties of the specific insulated glass unit, not simply the phrase "maximum mirror effect." Put on record which result matters most to you: a reflective facade, the view from inside, or natural daylight.
Coordinate the facade as a whole
Check separately how the glass looks in the doors, operable windows, and fixed sections. It is important to discuss visible profiles, joints between panes, and abutments in advance. If the project combines glass with wood, metal, or copper, material samples are best reviewed together.
A winter garden calls for a separate conversation
Do not automatically transfer a decision made for a residential terrace to an orangery. Prepare a list of plants and their care requirements, then discuss the glazing specification with specialists. An expressive facade should not become the sole selection criterion.
What to give the designer
Provide the site orientation, the level of privacy you want by day and by evening, lighting scenarios, the facade color, and the floor plan. Attach photos of the site and reference images with a note on what exactly appeals to you: the reflection, the tint, or the absence of visible fasteners. This turns a request to "buy a mirrored terrace" into a clear technical specification.