[Help!! New to designing 3d models, and Cura isn't working]

Thanks I've fixed it now! I assumed that it would figure out boxes drawn on top of boxes, but maybe not. I went inside the model and deleted every internal face, and then deleted every line on the model that wasn't an edge line. It now shows up perfectly in Cura

[Help!! New to designing 3d models, and Cura isn't working]

Hello,

I'm new to making 3d models in sketchup, and a little stuck.

I've made an object in sketch up by drawing shapes and push/pulling them to size, and then drawing further shapes on the existing model. I've used the Sketchup STL export ad on to export the file, but Cura really doesn't like it. Cura has lots of missing layers, and the X ray view shows lots of problems, but I just can't understand why it's not working given I drew the shapes on top of the existing shapes.

I've tried using meshlab to create the STL and that hasn't worked. I used MakePrintable to repair it and that just made things worse. There seems to be something fundamental I'm doing wrong, but have no idea what it is. Any ideas?!