There are lots of patterns for table runners that can be made as bed
runners. Either make more blocks for add more borders. I guess
you have to determine the size that you want and go from there.
Check American Patchwork and Quilting. They have lots of patterns
for table runners that would also work as bed runners. Or use a
quilt pattern and make it skinnier. Graph paper or spreadsheet
is your friend when you want to resize a pattern.