For residential, tile is attractive and functional; however it is also acceptable to leave concrete.
Cedar floors are an option, but is not intended as an alternative to tile.  Cedar "duckboard" is generally only installed in the walking area. It is mostly cosmetic for those who like the look.
If sauna is on a upper floor or over a wood subfloor, we recommend a water membrane and tile (as in a shower).
If floor is sloped, mosaic tiles are best.
You may add a tile baseboard up the wall 2-3".