How to make invisible roofs?

[AbullSinCara]

i am trying to make roofs on an building,but when i enter in,the roof doesn't disappear how to make is disappear when i enter?Because my levels are all without roofs,because you know i don't want to have my map details unseen because of an stupid roof who don't disappears.

 

[xxxRedMetalxxx]

You must go to tools and hit "new occlusion data"... if that does not work, make sure you "allow popping" on your roof. It's all in the tools section.