tiling angles

[jonnyp1]

i have bathroom in roof space want to tile round bath to ceiling for shower over bath. walls 12.5 plasterboard with bal tanking, 2 questions as i understand it this can normally take 32kg m2, 4 to 5 for grout/adhesive leaves 27 kg tiles, but would this be less as hanging at 45 degrees on pitch of roof, roof timbers 300mm spaces. would like to put 12mm travertine weighs just under 27kg. second question is there a standard way to line up the vertical back wall with the tiles on the pitch, or do have to cut several cms off each vertical tile to aligne with sloped tiles?
cheers jon

 

[tictic]

question mate ..this pitched roof...

is this under a staircase?.. if so dont tile it..

 

[jonnyp1]

no i live in flat in roof of old mansion so all my rooms have a small vertical stud wall upto rafters and then plaster board attached to inside of rafters to form rooms, so room looks like a triangle with the bottom corners cut off. my bath is against the gable end so i need to tile from the bath vertically up the gable and the vertical stud that makes roof space at each end of bath and then at 45 degrees from stud up angle of roof to top of room. so question is weight on angled bit and what is best way to keep alignment of tiles when on one wall vertical and other angle, a rise up the vertical of 600mm to keep alignment requres a rise up slope of 860, so do i just trim all vertical tiles?
cheers jon