There are many factors and considerations in order to answer this question accurately.
Unfortunately, I don’t believe a “normal bathroom install” actually exists. A comparison would have to be done regarding the current structure. There are just too many variables to be able to give you the answer you’re looking for. Chances are that your attic is not built to handle the added load (weight), either live or dead, of a new bathroom. That’s just one structural consideration. The location of the drain, waste and vent lines in the existing home will be a factor as well.
You should have someone qualified as a general contractor to give you their opinion based on the actual conditions.
Good luck.