Here's something that might help you:
http://www.fonsandporter.com/content...n_DECebook.pdf
or this:
http://www.maryquilts.com/wp-content.../Log-Cabin.pdf
I've tried using random length strips and cutting after attaching each log, and I've tried precutting the logs to the right sizes. I think my precut log blocks came out a little straighter, but it took a lot more time (for me) to cut up all those logs. But then again, I was going scrappy and I didn't want any duplicate fabrics so I had to make sure I had enough of each fabric in each log size, if that makes sense, and that was time consuming!