main thing to remember, lod1 is used by low gfx users so dont delete the inside walls in that or anything like that hehe. for lod1 just removal all the samll details, lights, cables etc
also never make the inside hollow ie, delete all in inside walls out without blocking off the windows in the LOD, nothing worse than looking at a building with a window from 500m away and seeing sky though it when looking into the building hehe.