HOW WE BUILD A BATTLE BOT
(click here)

Also check out
Building a robot.pdf

Here are some links for you on parts:

http://botbitz.com/shop/
http://www.basicmicro.com/Standard_c_18.html
http://www.hobbywing.com/category.php?id=89&filter_attr=5426.5599.0.0.5635.0.0.0.0.0

Wheels and mechanical parts (And some electronics)

http://www.robotmarketplace.com/
https://www.vexrobotics.com/vexpro
https://banebots.com/
https://www.fingertechrobotics.com/categories.php
http://www.sascootershop.co.za/electric-scooter-repairs.php
https://www.google.co.za/search?q=battery+isolator+switch
http://www.motionco.co.uk