Last year - 2015 /16 - our local quilt group gave the challenge for a BOM block using "Strips".
The block had to be 6" square, using any colour fabric and then put together in whatever way we liked.
Here is a photo of mine, which now needs to be quilted.
The next photo is this years challenge (also awaiting to be quilted )
We celebrate our ten year anniversary this year and our group name has the word "Green " in it.
Therefore the guideline was a 10" x 30" portrait wall hanging using the word "green " You could interpret that in whatever way you wanted, not necessarily using the colour green ( which I did )
Some of the ideas here for future challenges are really interesting and worth thinking about.