Good morning,
Let’s say that I have a pretty good experience of modeling under Gmax, 3DS and now Blender and that since 2007 and I always found that importing Sketchup models was a big problem because all the faces are imported: exterior and interior what is not desirable when one wants to create a model for FSX, P3D or MSFS.
Indeed these faces are very near and it occurs mostly flashes because the rendering engine tries to display everything that has been added to the model indiscriminately.
Nevertheless, if you still want to do it (there are cases where I do it despite these technical problems), it is better as Dimus said, export the model in DAE and then import it into Blender with the addon included DAE Import. For this there were free versions of Sketchup which allowed to read a SKP and to export it in DAE. I even think that there is now a way to expose in DAE only the external faces.
If once imported into Blender, the model still has duplicate faces, you must take your courage with both hands and try to select all the internal faces that you do not need (those that will never be visible) and remove them (for a shed with closed doors the internal faces are useless).
Before exporting to MSFS, you must at least create
ONE MSFS material and associate it with an element of the object: I create a Standard material in gray and I associate it with all the parts composing the object and I export for a test.
Then we can take the object and define as many MSFS material as necessary.
Good luck for your work