Here are some robot designs to give you ideas:
Botticelli, a simple robot.
Lucibot, which is Botticelli with a third wheel
COR3 from EV3Lessons
The EV3 Educator vehicle
DroidBot Jr design, from EV3Lessons
Driving BAS3, from EV3Lessons
More designs from EV3Lessons
Nigel Ward's list of robot design links
Then you need to think about attachments:
Robot Attachments Part 1
Robot Attachments Part 2
Attaching sensors
Making a Medium Motor Attachment
Simple Medium Motor Forklift attachment
How to lift an arm while moving
Building a Lift and Grab attachment |