The easiest thing would be to skew it up , but I tried it and well , it frankly looks horrific. And the textures don't align whatsoever.
I then tried copying the corridor and rotating it , but again that turned out sour with half of the things off grid. Unless I went to the ridiculous , painstaking levels ( and probably putting the R_speeds through the roof ) by cutting everything into triangles , then that wouldn't work either.
I've also tried a very quick job at doing the buttressess.
Doesn't look good in my opinion , if anything I need to 'trace over' the existing texture and make it metallic.