Nine roses: the vessel and the room it ends up in
Most bouquets are chosen in one place and lived with in another. Nine stems are large enough to need a decision about the vessel and small enough that the wrong one ruins the shape entirely, which makes this the count where the vase stops being an afterthought.
Everything below assumes the flowers are already good.
Geometry of the neck
A neck about as wide as the palm of your hand suits nine stems. The stems fan slightly. Each cut end sits in open water rather than pressed against its neighbours. The round top the florist built survives the move from paper to glass, which is what you are checking for. Lower the bunch in while it is still tied, and loosen the tie only once the stems are under water.
Narrow the neck and the bundle is squeezed into a column. The dome stretches upwards, the outer heads tip outwards at odd angles, and several stems end up drinking through a surface that is flat against the glass.
Go too wide without enough stems and the opposite happens. The bunch collapses to the walls, the middle empties, and the arrangement looks like it lost half of itself on the way home.
Height, weight and glass
As a rule the water should reach somewhere near the halfway mark of the stem, so a long cut wants a tall vase and a short cut a low one. Height alone is not enough, though. A tall vase with a light base tips the moment somebody brushes past it, and nine wet stems are heavier than they look.
Clear glass shows the stems, and that cuts both ways: it doubles the height of the arrangement visually, and it also shows every leaf, every bit of debris and the water going cloudy. Opaque ceramic hides all of that and reads as calmer, which suits a monochrome bunch better than a mixed one.
Where it sits
A round bouquet of this size looks right on a surface people walk past rather than sit at. A hall console, a chest of drawers, a shelf at chest height: the top of the dome is what you see, and it is the part built to be seen.
A dining table is the harder spot. Anything that blocks eye contact across the table gets moved during the meal, so a low wide vessel works better there than a tall one.
Kitchens are warmer than the rest of a flat and windowsills are the warmest place in them, which is why a bunch that seemed fine in the hall wilts in three days on a sunny sill.
Before ordering
It is worth knowing what the recipient actually owns. Plenty of homes have one narrow vase kept for single stems and nothing else, and in that case a hat box solves the problem at the source: the foam holds the heads, the water is already inside, and nobody has to hunt through cupboards during the first ten minutes of a visit.
Head size matters more than the number here as well. Nine large, densely petalled blooms fill a vessel that fifteen small ones would leave looking sparse, so the calibre is worth agreeing on when you place the order.
One more practical point for a delivery. If nine roses arrive while the person in Riyadh is out, ask a neighbour or a reception desk to stand the box upright rather than flat, because heads pressed sideways for several hours keep that lean afterwards.