SketchUp makes my head hurt.
If I WAS going to use SU and wanted to keep the workflow using free tools, I'd do the part drawings in DraftSight and then save them as DXF files for importing into SU. (http://support.google.com/sketchup/bin/answer.py?hl=en&answer=114366
You can download DraftSight from http://www.3ds.com/products/draftsight/free-cad-software/
- you have to "activate" it by entering your email address, "industry" and country. That's all there is to it. It can write and read the latest edition of AutoCAD DWG and DXF files (2010) and can save versions as early as Release 12 (WAAAAY back in the 90's!) of AutoCAD. I would _highly_ recommend it to anyone that wants a professional class tool for zero money.
If you're a college student (or have easy access to one) you could also buy Building Design Suite Ultimate 2013 Student for $150 which gets you a perpetual license to all the 2013 editions of AutoDesk products, including Inventor 2013 and AutoCAD 2013. If it was ME, I'd go this route, but I'm already an Inventor user and know how to use it. (At this point I have to plug the company that I bought my training material from, TEDCF Publishing - http://www.trainingtutorial.com.
They make an excellent product. I purchased the Inventor 10 series back in 2007.)
If you want a good, free parametric modeling tool, AutoDesk's 123D is an excellent choice - the only problem I have with it is that it currently doesn't have the ability to export to DXF/DWG nor import from there. It can however generate "laser sheets" that can be used for working with flat patterns. You'll have to check into it for more details on how that works.