If you prefer a pre-built sauna that requires only 1-2 hours of assembly.	If you would rather build from scratch requiring 2-3 days for construction but costing 20% less.
Modular Sauna	Kit Sauna
Pre-built in factory for inside OR outside use with optional custom room. Usually purchased as a portable solution of an anticipated move. Requires 1-2 hours for assembly. 240 volt 3 wire cable	Must build from scratch with 2 x 4 or 2x 6 stud shell of room or separate sauna building. Usually built as a permanent structure. Requires 2-3 days for construction. Approximately 20% less cost than modular saunas even if your hire a builder to install. 240 volt 2 wire cable

Once you have thought about the type of sauna you want to build,
you should give some thought to the size of the sauna.

Do you like to stretch out full length on the bench(s)?

If yes and under 5'11" in height and of average weight then a 5'x6' sauna will suit you and 3 others (all seated)	If NO to the stretching out option then the (4'x?') series may be right for you. A narrower bench means that all but the most petite of people will be sitting only. The (4'x?') series have 16" deep top and 13" bottom benches respectively, while the (5'x?') series and beyond have the optimum bench depth of 20 top and 17" bottom, you need to stretch out.
If yes and taller than 5'11" in height then the 5'x7' sauna is appropriate for you and 5 others (all seated)

That's all there is to it.

Other interesting facts to consider in the purchase of your sauna.

MODULAR sauna length and depth are slightly smaller than KIT saunas.

5'x6' and 5'x7' saunas are the most frequently purchased sizes.