The 1/2 bath in the house is currently located in the addition that joins the barn to the main part of the house. We are not keeping it in that location for a couple of reasons. The first reason is because its about as far away from the main living space as you can get. The second reason is its not easily accessible from the crawl space in order to run new plumbing.
My original idea was to put the bathroom under the main staircase since the staircase is basically floating. Toilets can go under a sloped ceiling since you are sitting back when you go to sit on it...basically this means you won't bump your head. There are a lot of really cool options for this kind of bathroom. I'm attaching a picture of one of my favorites.
Since then though, I've gotten to spend more time in the house and feel like the floating staircase is one of the coolest things about it. We've decided to keep the staircase as-is and put the half bath in what is currently a large closet just behind the stairs. Its not going to be a large half bath, but we really don't need a large half bath anyway. Also, I feel like in really old homes, like this one, its pretty typical to have a smaller half bath on the first floor (if you even have one at all!). The new bath is going to be similar to this picture which has always been one of my favorites. We will style the space a little differently, but this gives an idea of the goal.