You can be sure somebody has done it before, and I don't think it's hard, but you first need to be more specific about the LCD. This particularly applies if you have already got one.
There are two fundamental types
These are the ones you usually see on shields. They are referred to as 16x2 or 20x4 etc., being the number of characters and rows. I'm sure they can be used as a bar graph but it's probably not worth the effort.
These have a continuous cover of pixels rather than blocks of pixels to form characters. They are designated like 320x240, just like your computer screen. It is just as practical to to use them for text as graphs, even simultaneously.
It probably won't help much at the moment. but here is a link for a clock for the Nokia 5110 LCD. It is 84x48. The sketch is a clock with a bar graph for the seconds that I hope to eventually adapt to read power.http://blog.3d-logic.com/2012/08/26/digital-clock-on-arduino-uno-with-nokia-lcd-display/
and this might inspire you.....