I have made a couple in the past, but not with a strip pieced version. I just laid it out on the floor (before I had a design wall). To get an oblong instead of a square, just have more rows than columns. You want odd numbers of rows and columns so the design starts in the middle both ways. If for instance you used 5" charm squares to make it, you could do a 21 sq wide x23 sq long layout, which would finish about 94-1/2" x 103-1/2".
It helps to draw it out on graph paper. I've found that the center looks better in a mid tone, not a very dark or very light. Too dark or too light can look like a hole in the design.