Install them horizontally and offset I don't think you want any of your vertical grout line to have to line up in case the shower is not perfectly square.

Is your ceiling truly 108"? How high will the base be? Are you keeping the crown molding? You might not have as big a space as you though left over. I would go horizontal ( 48 wide ). You might only have 3" left over ( if that tile comes with a matching bullnose piece, then use that ) .

Good luck!

Thanks Debbi! The ceiling is 9' (haven't measured to see if it exactly 108"). I I wanted to run the tile vertical as I tend to like that better than horizontal. We haven't decided if we are going to keep the crown, the contractor suggested getting rid of it in the shower- thoughts? The tile does not have bullnose, so if I run it vertically would you put the small tile on the top or bottom?

Please post an image of the tile mounted vertically.

Even if you do that, your floor base may not be exactly level. Talk to your contractor about the issues you will encounter.

Example of Schluter edge around niche.

Example of Schluter edge on vertical and horizontal edge of exposed tile. There are lots of profiles, so it doesn't have to be this thick.

Following

IMO better to do a stacked horizontal layout in this case usually you lay the tile so the spot your eye naturally goes to is the spot with the fewest slivers I would tile to the ceiling and remove the crown in the shower area. I do not like niches so I would not do one but if you must then the advice to make sure yours is layed out to replace a tile is the best choice . I have never understood the need to display shampoo bottles and make the niche an accent tile IMO you use schluter edge where needed for a nice clean look and a nice modern over the door or wall caddy for bottles .

If you decide to go to the ceiling then do the smaller piece at the top. It's so high you probably won't even notice it once its all grouted.