Re: your log cabin idea
How about piecing a picture of a log cabin, in the middle of your log cabin block? By making the center picture rectangular, instead of square, you could easily obtain your 24" x 30", while keeping it just one block. Here's a block I made, years ago (for future sampler-type quilt). The block is actually square but I was holding camera at an angle, to eliminate a shadow. Anyway, you could make the center "picture" wider or taller, to turn it into a rectangle, then add as many rows of "logs" as you need, for size.
[ATTACH=CONFIG]434507[/ATTACH]