How much does it cost for a build out of a spa?

I am opening a spa and am trying to budget the build out. It is 1600 square ft vanilla shell. I am planning on a modern spa with a waiting area, reception desk, changing room, restroom and 4 treatment rooms. I've seen some articles that say $20-$35 a square foot depending on the finishes, but what does that all include? Is the design and cost of the architect included?