There's no standard to the size or shape of a bed runner, except to make it wide enough to be useful, and long enough to hang over the edges of the bed. I used a table runner for my basic pattern, and then I "graphed" it out on graph paper to adjust the sizes of the blocks, the number of blocks, etc. Just like a quilt pattern, so you know how much fabric, batting, etc. that you need, and the order to piece together the blocks. I seem to need that pattern in front of me to work well.
As far as using "cheater fabric", for heaven's sake, you're making it! Use whatever you want! I have used cheater fabric as the backing on a few quilts, and I like the look (as long as it goes well with the front).
Good luck to you!