Create two poly boxes for the roof halves, rotate them in place, then instead of having to worry about joining them just run the roof beam on top down the center 
Darkon
Red bellows of flame have blackened my stones
Convulsing my frame and cracking my bones
Hell's dragons of steel who roar in their chains
Crawl into my caves to suck out my veins.....
-The Mountain P.F.M.