So, shrad0 will teach you how to make custom models of your own without using other ROBLOXian's models.
How to make a Baseplate of your own:
You first pick anything you want, thats a block. Do not choose the truss beams or the wheels or the balls. Pick something BLOCKY. Then click on Resize.
Heres a Plastic Green brick being resized:
Now you've made the baseplate!
Now watch a tutorial from Shedletsky:
www.youtube.com/watch?v=Pwl_purY&feature=c4=overview=vl&list=PL179F5CBDF46F8E4