Like commo said - you need to try to find a location near an existing sanitary waste line f you want to keepcosts under control - utility closets and toilet rooms are good places to start - also look at the existing plumbing drawings of the floor below the one you want the shower on - thats where the waste piping for the floor above will show. Remember that this is sanitary waste and can't be tied into the roof drains. If your building has a grey water system, you might be able to tie into that.
Adding a shower to a floor above grade or above a crawl space will be considerable easier than adding one to a slab on grade. You can core the floor, depending on your local or state plumbing code you may also need an overflow drain, and do the drainage connection in the ceiling of the floor below. In a slab on grade application you will need to tear up the flooring, trench the floor, do your waste connection, backfill, repour the slab and finally replace the flooring.
Finally, you will likely need to get architectural, plumbing and HVAC drawings (shower rooms are required to be vented, typically can be connected to toilet room exhausts) before the building inspector will issue a construction permit.
Good luck.