Honestly, the best setup isn't one fancy furniture piece—it's a mix of lightweight, weatherproof, movable pieces that can handle wind, sun, and lots of different people. Since your garden already has raised beds, you need furniture that supports chatting, resting, potting, and storing tools without crowding the beds or blocking sun.
Start with modular benches. Powder-coated aluminum or galvanized steel frames with FSC teak, acacia, or recycled HDPE slats are ideal. They're tough, won't rot, and are much lighter than cast iron or concrete. Choose backless benches that can tuck under raised-bed edges, or benches with a slight back for older volunteers. If the beds are tall, a bench-height 18–20 inches works well; for kids or accessible seating, add a couple of 24–26 inch perch stools.
Storage benches are a community garden MVP. You can stash trowels, gloves, hose fittings, and cushions, while the top gives extra seating. Just make sure the lid is self-locking or gas-strut supported so it doesn't slam in the wind.
For flexible gatherings, add two or three lightweight bistro sets. Aluminum or HDPE chairs with mesh or sling seats dry fast and won't blow away as easily if they're stackable and you bring cushions inside. Avoid glass tabletops and heavy umbrellas unless they're anchored properly. A small side table or two is more useful than one big table on a rooftop.
Don't forget wind. Rooftops are gusty, so look for furniture with weighted bases, locking casters, or anchor points. If you use wood, choose rot-resistant species and oil it yearly. For cushions, use solution-dyed acrylic or olefin with quick-dry foam, and store them in a deck box when not in use.
Finally, think about accessibility and flow. Leave at least 36 inches between raised beds and seating so wheelchairs, wagons, and wheelbarrows can pass. Mix movable chairs with a few fixed benches along the parapet or pergola. That way the garden can host a quiet morning coffee, a volunteer workday, or a community workshop without feeling cramped. In short: powder-coated aluminum or steel frames, teak/HDPE slats, storage benches, stackable bistro sets, and wind-smart accessories. That combo is the sweet spot for a community rooftop garden with raised beds.