Saw this posted on the Breathe forums and it's quite important for those of you who don't know it. It was about building large objects. I'll post it here:
Maximum number of geometry components is 128. after that they are ignored.
Maximum size of any geometry LOD is 64 meters. Beyond that and it is ignored.
For an aircraft carrier you must make it in sections.
and you dare not let geometry handle your walkways. you must use roadway LOD for that, ensuring that the roadway is slightly above the geometry.
For greatest effectiveness, use roadways for all horizontal surfaces and only use geometry to prevent crossing of walls. No need for geometry below a flat surface, because you will be walking on the roadway.
proximity of geometry to any place you wish to walk will cause jittering.