One tip with Sketchup; later on down the line, when you're ready to export the model to Pepakura, you're going to want to make sure the faces are all oriented the same. For example, in your picture, part of the model is white and part of the model is light blue, you're going to want a uniform color on the outside (in this case, white). To do this, right click on the face you wish to invert, and select "Reverse Faces." If you have a mixture of faces on one side of the model, it will affect the Pepakura model.