From inside sketchup, goto file import and then search for sbr20 and up pops a linear rail, bearings and mounts component.

If you can't find something inside of sketchup try a google search for 'rm1605 ballscrew sketchup' and download the file onto your computer, then you can import it into sketchup from your computer.

To be honest it seems a little odd to buy all the parts first with no idea about how to arrange them into a working machine and then start trying to figure out how to do it with no money for making mistakes and no time to learn how to do things.

If you take a look at the build logs most people seem to take many months to assemble their first machine, it might be best to put a plan together first either properly done technical drawings on paper or a CAD model that way people here will find it much easier to help you.

I'm just starting to put together a plan for my own first build and from most of the information I've garnered it seems that 20mm plate is fine and the top & bottom rails on the gantry is quite popular.

Try reading this thread, it has CAD drawings and photos to help you visualise:
http://www.mycncuk.com/forums/diy-ma...gn-advice.html