A small powder room is what it is - you aren't going to make it feel like a football field no matter what you do! I've seen large tiles in small baths that look great and I've seen really small tiles that look great (we're doing a mosaic in our powder room at the moment) but I don't think they really do anything to make the space feel bigger one way or the other. And even the middle of the road size like subways look good. About the only thing I don't care for are the old 4 x 4's but that's a personal preference and there are probably new ones that could make me change my mind.

I would tend to agree that tiling just 1 wall half way up might look unfinished or like you ran out of tile or money. But I also think tiling 3 of 4 walls would look more unfinished. Personally, I would either tile all 4 or none. Or I might consider tiling 1 wall all the way up with a really stunning tile. As already stated, it's really a matter of personal preference. Have you seen it? You mentioned that your builder thought it looked unfinished. Do you?

Thank you for your help. Here are the after pictures excluding decorative accents. Wall paint BM Palladian Blue, floor tile 12"x3" grey marble polished porcelain, accent wall tile 24"x12" white marble polished porcelain with white marble stone pencil border.

IMo the better choice would be a simple stacked pattern floor I don't think herringbone with a border is going to have any effect in such small space. Make the space more interesting with wallpaper and the decor it will have a much bigger impact that the floor.