Another thing I have found with Blender and uploading Collada from it is, manually triangulate your mesh within blender and disable the option in the upload settings in blender "Triangulate Mesh". I have found that SL triangulates it automatically if it doesn't like the way it was triangulated. This way you can also see if you have any extra verts where they should not be and gives you an idea of where the small triangles are.
Where SL has troubles with buildings is if there are a lot of doors and windows. Also, when you build your physics model be sure to delete any surface on the tops and bottoms of all doors and remove all surfaces inside the windows, so you are only left with inside and outside walls. And all doorways remove the headers as you will not be walking above the door opening lol.
This is how I find the easiest and best way of making buildings and exporting to SL thanks to all the great help from these forums. Your physics model has to be as simple as possible to cut down on LI.