Sauna design gets discussed as a look and is really four functional decisions: where the benches sit relative to the heat, how air moves through the room, where the light comes from, and what the surfaces you touch are made of. Get those right and almost any aesthetic works. Get them wrong and a beautiful cabin is unpleasant to sit in.
Bench geometry against the heat
The upper bench should be level with or above the top of the heater stones, with a modest gap to the ceiling, so you sit in the hot layer rather than under it. Everything else about the plan follows from that: ceiling height, the number of tiers, and how much floor is left. This is the decision that most separates a designed sauna from an assembled one.
The heat path
Air in low near the heater, out high or low on the opposite side. Without a path the lower bench stays cold, the air goes stale and the cabin never dries. Vents are small, cheap and invisible in a finished room, and they are the most commonly omitted element in a self build and in imported prefab cabins alike.
Light
Indirect and low. A rated fitting under the upper bench or behind a timber shade gives a room that feels warm; an overhead fitting in your eye line does not. Cabins with a glass front get light from the room outside and need less inside. Anything battery powered or plastic does not belong in there.
Materials and restraint
Low density knot free timber where skin touches, no metal you can reach, no sealed finishes inside, and glass in tempered safety grade. Beyond that, aesthetics are free: dark thermally modified cladding, pale aspen, a glass front, a panoramic end. The constraint list is short and none of it limits how the room looks.
Questions people ask about sauna design
What is the most important design decision?
Bench height relative to the top of the heater stones, with a modest gap to the ceiling. Everything else in the plan follows from it.
Do vents really matter?
Yes. Without an air path in low and out on the opposite side the lower bench stays cold and the cabin never dries properly.
Does a glass front hurt performance?
It loses more heat than timber, so size the heater accordingly. It is a legitimate choice, not a mistake.