I've done a couple mesh buildings so far and there are some really nice benefits to building it 100% in blender both technically and artistically. I'll go ahead ang give some tips even if you don't want em or have already heard this stuff a million times:
1.Use a seperate ultra low poly proxy object for the physics
2.Use multiple materials for inside and outside for example
3.Unwrap it well so the textures look great in SL, an AO bake can do alot for the process
4.Keep it modular, think of parts that could be reused and instanced (copied) in SL ie window frames, upload as seperate objects to reduce the overhead.