I,m in England.
OK, so before you start anything. Read this: //www.diynot.com/wiki/electrics:part_p:diy_electrical_work_and_the_law
It says that to do electrical work in a bathroom you have two choices:
1. If you are planning to do it yourself, you must contact your local authority building control at least 2 days before starting work. Fill in their forms and pay their fee.
They will inspect and approve the works done (if it has been done to BS7671). You may need to add an RCD to the lighting circuit and/or provide supplementary equipotential bonding.
or
2. Get a registered electrician to do the work. You can find a local one at www.competentperson.co.uk
also
There isn't a loft or anything else above the bathroom.
Is it a flat roof or something? If so, how are you going to recess the lights and run the wiring between them?
You'll need a good 6" clearance above them.
I hope that they are the sealed type otherwise they will pull steamy air into the ceiling space and you will get damp = rotting of ceiling timbers.