Empty space in model is getting filled
I suspect, as I am wont to do, that your problem lies in the STL created by SketchUp. It's an unfortunate aspect of that program that it creates non-manifold models which creates troubles such as this. 

Consider to load your STL file into a program suitable for showing flaws (and repairing them) to determine where the failure points lie. I'm fond of Meshmixer, but there are many others such as Netfabb with which I am less familiar.

If you don't want to check your STL file, attach it to your post and I'll take a shot at it. 

You would also want to consider to learn a new program if you intend to perform such 3D modeling. Fusion 360 has a popular following. I'm a fan of OpenScad, but use Fusion 360, Meshmixer, Blender (only a tiny amount) and anything else I can utilize for model repair, creation and editing. Build a large repetoire of different programs and get the best of all worlds.

SketchUp has a strong following primarily because it's rather easy to use. The same can be said of a few other programs, but SketchUp really generates trouble when it comes to 3D models.

TinkerCAD is very much like SketchUp and will give you better final results. OnShape is another popular modeling program, but I have zero exposure to that one.

It's not out of the question that there's a bug in Cura that's causing this problem. You are not limited to one slicer program, and you can check the results of another slicer such as Slic3r, Craftware or others.