The short answer is to make the furniture heavier, tie it down, reduce the wind hitting it, and remove anything loose before a storm. On a rooftop, wind is usually stronger and more turbulent than it is at street level, so what feels stable on a balcony can still slide, rattle, or flip. I would start by walking the roof on a windy day and noticing which corners and gaps funnel the wind. That tells you where to place the heaviest items and where you need a windbreak or anchor points.
Choose furniture that is designed to stay put. Heavy cast aluminum, concrete, stone, or solid teak pieces are much better than hollow plastic or lightweight resin. If you already have light chairs and tables, weight them down rather than replacing everything. Sandbags, water weights, and heavy planters can work well, but make sure they are secured to the furniture or placed so they cannot slide off themselves. For tables, a weighted umbrella base is not enough if the table itself is light; use table weights or straps that wrap around the top and legs.
Anchor what you can. Metal eyelets, adjustable straps, and carabiners can connect furniture to a sturdy railing, a fixed structural point, or dedicated anchor rings. Never drill into a waterproof roof membrane or tie to something that may pull loose. If you rent or manage a building, check the rules first and ask maintenance what is safe to use. For chairs, a simple strap through the frame and around a heavy planter can make a big difference. For sofas and loungers, use a cover with a tight fit and strap the whole piece down, because a loose cover acts like a sail.
Reduce the wind with a barrier. A glass or solid windbreak, a trellis with dense planting, or a row of heavy planters can slow the airflow before it reaches the seating area. Do not block drains, fire exits, or ventilation, and make sure anything you add is itself anchored. Cushions, throw pillows, and lightweight trays should be stored in a locked bench or brought inside when strong winds are forecast. Small items are the first things to go airborne, and they can cause damage or injury.
Finally, build a quick wind routine. Check the forecast, stack or fold light chairs, lock casters, close umbrellas, and put away loose decor. If you live in a very exposed building, consider stackable or folding furniture that can be moved into a storage cabinet. The goal is not to fight the wind every day; it is to set up the roof so the furniture has weight, attachment, and less exposure when the wind picks up.