I doubt you can build one as cheap as this;

http://www.amazon.com/Crosse-Technology-BC-900-AlphaPower-Battery/dp/B00077AA5Q/ref=pd_bbs_1?ie=UTF8&s=home-garden&qid=1223900977&sr=8-1

I own one of these, I love it. Before purchasing this, I had stopped using rechargeable batteries, because I never knew which ones were good, how to match them up, etc. With the refresh or test cycle on this thing, it tells you the capacity. It's been very good at bringing questionable batteries back to life. It does not have a way to connect to a PC, but it does have 4 separate channels, and all parameters can be set per cell (charge current, discharge current, etc.)

Even if you get a schematic for such a device, you are still not going to have the software that is used to control it. A charger like this has to have a microcontroller with suitable code to run it.

Tom