An outdoor dining set has to survive weather and also work as a table, which pulls in two directions. Tabletop material, seat count and how the set stores through winter matter more here than in any other outdoor category.
Tempered glass looks light and cleans easily but shows every water spot and can shatter if it takes a hard knock. Slatted HDPE or aluminum sheds rain through or off, needs no sealing and will not crack. Wood tops (eucalyptus, acacia, teak) look best and ask the most: annual sealing if you want them to stay brown rather than weather to grey.
A seven-piece set is conventionally a table and six chairs, but confirm that from the listing rather than assuming. The more useful question is where the chairs go in winter: stacking chairs solve a storage problem that identical non-stacking chairs create.
A centre hole is easy to ignore at purchase and impossible to add later. If you have any intention of shading the table, buy the table that accommodates it and check the hole diameter against the umbrella pole.
An extendable or butterfly-leaf table lets a six-seat footprint host eight occasionally, without giving up the deck space year-round. The trade is more moving parts exposed to weather.
If the set will live uncovered through a wet winter, weight the frame and tabletop decisions harder than the cushion decision: cushions can be replaced, a warped tabletop cannot.
More depth: how the five common materials fail and what weather ratings actually commit a seller to.
Allow roughly 24 inches of table edge per person, and at least three feet of clear space behind each chair so people can push back and stand. A round table seats more people in a tight footprint than a rectangle of the same area, and makes conversation easier.
Not inherently, tempered glass is standard and safe, but it is the top most likely to be damaged, hardest to keep looking clean, and worst in high wind if the table is light. Slatted HDPE, aluminium or wood are lower-maintenance choices for exposed spaces.
HDPE and teak can, and aluminium frames can. Steel frames and any set with fabric or cushions do better stored or covered. The specific failure to avoid is water sitting inside a hollow frame and freezing, so check that legs and tube ends drain.