You can't embed SketchUp files directly, you have to upload the models to Sketchfab first:
https://sketchfab.com
You can either export from SketchUp to a .DAE or .KMZ file and upload that, or use the Sketchfab export plugin for SketchUp:
https://sketchfab.com/exporters/sketchup
Once the model is uploaded, you can just paste the model URL into the post and it'll get embedded automatically:
via Sketchfab