when you import CAD files into SketchUp you'll see a little 'options' button in the bottom right corner of the file import dialog box. click on the options button and when you've got the options dialog open you'll see a drop down menu for the scale of the default unit of measurement of your CAD file.

You mentioned that your CAD files are too small. Typically that ends up being the case if your CAD file units are feet and you select inches as the scale option. The end result is that your CAD file will be 1/12 the original size since 1' will be equal to 1".

try choosing the option for setting the units equal to feet and see if that helps. 

-mike