Either get an already fabricated module, or buy an Accelerator IC, read the data sheet and hook it up. _Then_ if you have questions, come back. The question of how to make an accelerometer for a robot, is WAY to broad.
You could always hang a weight from a string and measure the angle of the dangle with a protractor.
Or, if you want to measure the acceleration due to gravity, then do what the Tom Baker Dr. Who used to do when he would "land" on a strange planet--whip out your yoyo and gauge the fall and rise rate.
I would also suggest buying one. I don't think that it's a good idea to make your own one, I personally didn't know where I would have to start. But the fabricated ones are very good and I can recommend the CHR-6d Inertial Measurement Unit! It's not even expensive! You should check it out!
